Iceplant is a halophyte with two different photosynthetic modes of C₃ and crassulacean acid metabolism (CAM). Environmental stress, such as a high salinity condition, is known as a trigger for shifting the photosynthetic mode from C₃ to CAM in a plant. The application of 6-benzylaminopurine to cell culture medium was effective to induce green calli from leaves of C₃ and CAM plants. The photosynthesis of greened calli obtained from C₃ and CAM plant leaves showed low temperature adaptation and wide temperature adaptation, respectively. In the calli derived from the C₃ plant, the activity of ribulose 1, 5-bisphosphate carboxylase (RuBPCase) was higher than that of phosphoenolpyruvate carboxylase (PEPCase), while in the calli from the CAM plant, the activity of PEPCase was higher than that of RuBPCase. Thus, the greened calli showed the original levels of enzymatic activity in their donor plants. The activity of PEPCase in the greened calli obtained from the C₃ plant increased with the application of NaCl to the cell culture medium, but this effect was not detected on nongreened calli.

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Genotype×environment interactions of grain yield in rice were estimated for early-maturing cultivars with high palatability. Genotype×year and genotype×location interaction of yield were significant. On the other hand, genotype×cropping season and genotype×amount of fertilizer interaction of yield were not significant. Regression coefficients obtained by Finlay-Wilkinson's method for evaluation of adaptability were the same for newly bred cultivars as check cultivars. There was only a slight difference found between newly bred cultivars and check cultivars in yield. No significant correlation was found between yield and palatability. These results show that varietal differences in yield differ under different environmental conditions as year and location and yield tests conducted under different years and locations were essential. Newly bred cultivars had the same adaptability and yield ability as high palatability check cultivars.

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Genotype×environment interactions of heading date and culm length in rice were estimated for cultivars with high palatability. Genotype×year, genotype×location, genotype×amount of fertilizer and genotype×cropping season interaction of heading date were significant. Though it was significant owing to small experimental error, the change of Varietal difference in heading date under different amounts of fertilizer was very small. Genotype×year and genotype×location interaction of culm length were significant. Genotype×cropping season and genotype×amount of fertilizer interaction of culm length were not significant. Regression coefficients obtained by Finlay-Wilkinson's method for evaluating the stability of heading date and culm length were the same for newly bred cultivars as check cultivars. These results show that new cultivars with high palatability can be recommended by assuming that the difference in heading date from check cultivars may not differ according to the amount of fertilizer or in culm length according to the amount of fertilizer or cropping season.

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Rice cultivars Akitakomachi and Hitomebore were cultivated in the field using an on-farm developed system ; no basal dressing of nitrogen combined with sparse planting (Exp plots). Their growth and yield were analyzed as compared with rice cultivated by general practice (Cont plot) with respect to the improvement of yield. In the Exp plots, nitrogen application was omitted at basal dressing but carried out as top dressing from 8th leaf age onward. Compared with the Cont plot, leaf expansion and tillering in the Exp plots were slower, the maximum leaf area index being about 4, whereas it was about 6 in the Cont plot. In the Exp plots, the percentage of fruitful culms was relatively large, but the panicle number m^-2 was small, which resulted in a small spikelet number, less than 30, 000. The percentage of ripened grains was significantly larger, but the yield was 5-10% lower than that of the Cont plot. The panicle number per hill of primary tillers was not largely different among the plots, but that of secondary tillers was relatively large in the Exp plots. The fruitful culms of both primary and secondary tillers appeared to develop from upper node orders in the Exp plots as compared to the Cont plot. The panicles of secondary tillers in the Exp plots were larger than those in the Cont plot with respect to panicle weight, panicle length and leaf weight per panicle. Relative light intensity in the canopy was significantly larger at both booting and middle ripening stages in the Exp plots as compared to that in the Cont plot.

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Simplified investigation methods of root systems in Japanese and American rice cultivars were examined using photographic recording methods and image analysis on a personal computer. In order to photograph flat expanded root systems, plastic boards were inserted vertically into the soil and culture boxes before seeding or planting in each experiment. Each root system profile picture was divided into parts every 5cm from the plant and at an angle of 22.5°from the horizonal. The ‘center of root system gravity' [CRSG : integrated (PV×RPA)/the sum of RPA)] and 'moment of root system' [MRS : integrated (PV×RPA)] were calculated as indicators of root distribution using the 'position value' (PV : the distance×the angle) and the 'root projection area' (RPA) in each part. In field experiments, cultivar differences in root system profiles were revealed easily, and all American cultivars except New bonnet showed a tendency of deep distribution and large root quantity (CRSG : Lemont > New bonnet ≧ M - 401 > M - 7 ≧ Ishikari > Nipponbare > Tsukinohikari ≧ Nakateshinsenbon, MRS : M-401 > M- 7 > Lemont ≧ Nipponbare > Nakateshinsenbon ≧ Tsukinohikari ≧ New bonnet ≧ Ishikari). In large root box experiments, it was possible to obtain the values of CRSG and MRS similar to those obtained in the field experiments ; however, it was difficult to evaluate numerous cultivars owing to the high cost of root boxes and troublesome management. In small plastic root boxes and water culture experiments, it was not possible to obtain accurate values for them.

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The effects of supplying reflected light on the photosynthetic rate of middle and lower leaves and on the seed yield of soybean were investigated. Soybean cultivar Suzukari was grown in Wagner pots and in an upland field. Reflected light was supplied by covering the surface of the pots with aluminum foil in 1994 and with reflected sheets between rows in the field in 1995. Light reflection treatment was carried out from the flower bud differentiation stage to maturity in both years. Photosynthetic rate, transpiration rate and stomatal conductance of the middle and lower leaves (4th to 6th leaves) were measured under natural light. The higher the leaf position was, the higher the photosynthetic rate of the pot-cultured plants at high light intensity (over 1000μmol m^-2 s^-1). The photosynthetic rate reached its maximum in the flowering stage. This was followed by a gradual decrease with plant age. The photosynthetic rate of middle and lower leaves appeared to be correlated to light intensity at low light intensity and the rate of CO₂ diffusion through stomata at high light intensity. Reflected light caused an increase in the photosynthetic rate of middle and lower leaves. In the field, reflected light intensity was increased between rows in fine weather and between plants within a row in cloudy weather. The photosynthetic rate and seed yield in the field were little affected by reflected light.

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The higher number of spikelets in modern rice varieties with higher yielding ability (MVs) results from the higher number of secondary rachis branches (SBs). It is conjectured that rice cultivar Takanari has higher ability to develop more spikelets at upper part of a panicle and that it realizes greater grain-filling ability. The experimental objective was to clarify the varietal difference in nodal distribution of SBs and spikelets on a rachis (ear type) between local japonica varieties (LJVs) and MVs. Eight cultivars different in the number and the size of spikelets were used. The cultivars were classified into three ear types with differentiated spikelets : Spikelets on middle modes superior-type, spikelets on middle and lower nodes superior-type and spikelets on lower nodes superior-type. The cultivars of higher spikelet number except Akenohoshi differentiated SBs mainly on lower nodes. The increased SBs on lower nodes were, however, easily degenerated. This made survival spikelet number at the middle part of a panicle increased more than that at upper and lower parts with the exception on Nanjin 11 and Arborio. There was little difference in ear type between local and modern japonica varieties. Spikelets at the upper part of panicle in LJVs could not supplement the loss of spikelets degenerated at the lower part. It was concluded that it is difficult to increase spikelets at the upper part, using the LJVs researched in this experiment.

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The effect of time and rate of nitrogen application on root growth and their relations with constituents of top per hill were investigated using Chinese F₁ hybrid rice (cv. Shanyou 63) under water culture conditions. Treatments of several nitrogen rates were applied in three growth stages : early growth stage (before 14.5 Plant age in leaf number), middle growth stage (13.5 to 17.0 plant age in leaf number), and late growth stage (17.0 plant age in leaf number to maturity). The number of crown root primordia and emerged crown roots, root dry weight, and some constituents of top per hill were investigated. In the early growth stage, root dry weight per hill increased as nitrogen concentration increased, and correlated rather with the root number than with the mean dry weight of root axis. In the middle growth stage, root dry weight per hill decreased with the increment of the nitrogen rate, especially in the roots of the upper three nodes. In the late growth stage, root growth was largely affected by nitrogen application during the middle growth stage, while little effect of the nitrogen rate was observed in root dry weight. The increment of root dry weight per hill in the middle growth stage was the largest followed by that of the early growth stage, and only a slight increment was observed in the late growth stage. High positive correlations were observed between the number of crown root primordia and the concentration of nitrogen of the top per hill at the crown root primordia differentiation time, and between the emergence rate of the crown roots and the concentration of starch at the time of emergence. From these results, it is believed that nitrogen and carbohydrate are the factors that promote the differentiation of crown root primordia and the emergence of crown roots, respectively.

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Reductions of growth and symbiotic nitrogen fixation were studied in soybean exposed to simulated acid rain (SAR) applied to different sites. Soybean cultivar Okuharawase was grown in 1/5000a pots under a rain shelter. The plants were exposed to SAR from 15 days after sowing (DAS) to the flowering stage at 36 DAS. The sites of SAR application were foliage, soil and both foliage and soil, and the pH of SAR used was 2.7, 3.5, 4.5 and 7.0 (control). At the flowering stage, leaf area per plant, apparent photosynthetic rate and root dry weight per plant decreased in proportion to decrease in the pH of SAR. The degree of decrease was similar between the plants exposed to SAR in foliage and soil and those in foliage, but the application of SAR to soil alone did not cause any change in the parameters. There was a consistent reduction in the number of nodules per plant, the fresh weight of nodules per plant and the rate of symbiotic nitrogen fixation, or acetylene reduction activity (ARA) regardless of the site of SAR application. ARA decreased in proportion to the decrease in the number and fresh weight of nodules. The root dry weight significantly correlated with nodule number or nodule fresh weight. The reduction of growth and symbiotic nitrogen fixation in plants with exposure to SAR in foliage was similar to that with exposure in both foliage and soil, whereas SAR applied to soil alone suppressed modulation only.

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In order to investigate the possibility of introducing lodging resistance into long culm and ear weight type rice cultivars, we studied the genetic characteristics of breaking strength related to lodging resistance in a cross between Koshihikari and Chugoku 117 with small and large section modulus, respectively, and their progenies. In the F₁ plants, the mean section modulus was much higher than that in Koshihikari, while the mean of the bending stress was higher than that in Chugoku 117 as well as that in Koshihikari. Consequently, the mean of the bending moment at breaking of the basal internode (M) in the F₁ population was much higher than that in Koshihikari as well as Chugoku 117. The M in F₂ ranged widely from 800 to 2900 g cm, and eight plants of F₂ exceeded the maximum value of Chugoku 117. The section modulus in F₂ ranged widely from 8 to 25 mm³ and showed a trimodal frequency distribution. The ratio of 30 : 92 : 28 did not fit the 1 : 2 : 1 expected for one-gene segregation. The section modulus showed a comparatively large heritability value in the F₂ line, so this character was expected to be effective for selection. Despite negative genotypic correlation between section modulus and bending stress, three plants in the F₂ line had very high NI values due to large section modulus and large bending stress. The M and section modulus in the two F₃ lines were almost large, corresponding to the selected F₂ parental plants. From these results, there is a possibility of introducing lodging resistance into long culm type cultivars by individual selection.

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Every successive cross section in the unelongated portions of the main stem of five rice cultivars, 8.5-8.6 plant age in leaf number, were investigated anatomically to clarify the varietal differences of some characteristics on the formation of crown root primordia. (1) The number of emerged crown roots per plant were larger in IR36, Nipponbare and Fujiminori followed by Koshihikari and Akenohoshi. These orders coincided with the orders of the number of tillers. (2) The order of the number of crown root primordia of the main stem was IR36 > Fujiminori, Nipponbare > Koshihikari, Akenohoshi. But, the diameter of the base of the crown root primordia was smaller in cultivars with more crown root primordia. There were no correlations between the total number of crown root primordia and the length of the stem or the area of peripheral cylinder of longitudinal vascular bundles. However, when the stem was divided into successive 'units' as previously reported, a significant positive correlation was found between the number of crown root primordia and the area of peripheral cylinder of longitudinal vascular bundles. The percentage of the formation of the crown root primordia indicated by the linear regression coefficient was higher in cultivars with more crown root primordia. (3) These results suggest that the number of crown root primordia of the main stem is larger in cultivars with more tillers and/or with more emerged crown root per plant, and also in cultivars with diameters less than the base of the crown root primordia.

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It was clarified in a previous paper that higher dry matter production for a newly bred high-yielding rice cultivar, Takanari was mainly due to the higher net assimilation rate (NAR) owing to better light-intercepting characteristics after the panicle formation stage. The CO₂ exchange rate, which affects the NAR, was studied using cultivars, Takanari and Nipponbare in this paper. Observations showed that Takanari was remarkably higher in CO₂ exchange rate than Nipponbare during diurnal courses, during leaf- senescence or at different leaf positions. These results indicate that the higher NAR for Takanari was due to not only better light-intercepting characteristics but also a higher CO₂ exchange rate. Furthermore, the cause why these differences in photosynthesis existed between the two varieties was examined. It was found that the CO₂ exchange rates for Takanari maintained a higher level owing to its higher diffusive conductance during diurnal courses, and owing to both its higher diffusive conductance and higher photosynthetic capacity during leaf senescence. Further investigation indicated that the higher photosynthetic capacity for Takanari was mainly owing to a higher apparent carboxylation efficiency and Rubisco content during leaf senescence.

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PCR amplification of cDNA prepared from the poly (A)⁺ RNA of tuberous roots of sweet potato, using degenerate oligonucleotide primers based on highly conserved regions among sucrose synthase (EC 2. 4. 1. 13) reported previously, yielded a cDNA of 1, 191 bp (IBSUS). The nucleotide sequence of IBSUS exhibited a high degree of homology with the corresponding regions of the potato sucrose synthase cDNA sequences (82 and 86% of identical nucleotides). Less homology (76∼77%) was found in the monocotyledonous sequences (maize, rice and barley). The activity of sucrose synthase in the tuberous roots of sweet potato was higher than that in other parts, namely, leaf blades, petioles, stolons and fibrous roots. The activity of sucrose synthase in roots increased markedly following an increase in sucrose during development of the tuberous roots. Northern blot analysis using IBSUS as a probe revealed that a signal of sucrose synthase mRNA with a size of approximately 2.4 kb was present in petioles, solons, fibrous roots and tuberous roots, and the levels of sucrose synthase mRNA in different parts and in the roots during development of tuberous roots were highly correlated with enzymatic activities. In petioles, an increase in sucrose concentration led to an increase in the activity of sucrose synthase.

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Field experiments were carried out to clarify the differences and key factors in the rate of seedling establishment among rice varieties sown on the soil surface in flooded paddy fields. The percentage of seedling establishment in flooded paddy fields with average temperatures of 17.9 and 22.7°C using 7 varieties of rice (4 Japanese, 1 Portuguese, 1 Chinese and 1 Hungarian) varied from 18 to 94% with a significant varietal difference. The main causes for lower seedling establishment rate existed in floating and seedling mortality in the younger stage. These two causes were independent of each other, and their relative importance differed among varieties. The percentage of floating seedling in cv. Arroz da Terra was relatively low compared with other varieties. No clear correlations were found between the percentage of floating seedling and the plant length, the seminal root length or the apparent weight of seedling underwater. It was presumed that the varietal difference in the percentage of floating seedling might be caused by differences in the rooting abilities into the soil up to the 2nd leaf stage.

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The relationship between growth respiration and nitrogen content in rice organs was investigated. Top and root CO₂ exchange rates were continuously measured for 5-6 days under different nutrient concentrations by lowering the light intensity with each passing day. There were significant positive correlations between the growth respiration rate in the top (Rgt) and dry matter increase in the top, and between the growth respiration rate in the root (Rgt) and dry matter increase in the root. Though, there were significant positive correlations between Rgt and leaf area expansion, and leaf dry matter increase, no significant relationship was found between Rgt and dry matter in leaf sheath. The growth respiration rate in each plant part was closely related to the dry matter increase and nitrogen increase. The nitrogen content of the leaf blade was higher than that of the leaf sheath. This suggests that growth respiration in the top is utilized more for the growth of leaf blade than that of leaf sheath. Moreover, the ranges of growth coefficient in the whole plant, top and root were from 0.56 to 1.26, 0.44 to 1.11, and 0.60 to 1.11 g g^-1, respectively, under different nutrient conditions. The growth coefficient of each part increased as the result of nitrogen content in new biomass. The growth coefficient in the root was higher than that in the top when compared at the same value of the ratio of the increase in nitrogen. The slope of linear regression in the root was higher than that in the top. In this paper, it was determined quantitatively the relationship between nitrogen increase and growth coefficient in rice organs.

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To elucidate the physicochemical properties of Japanese native red-kerneled non-glutinous rice of the Japonica type cultivated without fertilizer application, a comparative study with 30 cultivars was made on the protein content, amylose content and amylographic characteristics of milled rice and the textural characteristics of cooked rice. The protein and amylose content of the red-kerneled rice used ranged from 6.0 to 9.7% and from 9.7 to 26.4%, respectively. These values for the Fukuoka Prefecture recommended variety (white-kerneled rice) used ranged from 6.5 to 6.9% and 15.6 to 20.9%, respectively. The maximum viscosity and breakdown values of the red-kerneled rice ranged from 170 to 545 B.U. and from 0 to 173 B.U., respectively. In the white-kerneled rice, these values ranged from 368 to 615 B.U. and from 68 to 235 B.U., respectively. The adhesion and hardness / adhesion ratio of the red-kerneled rice ranged from 0.00 to 0.29 T.U. and from 0.00 to 842.00, respectively. In the white-kerneled rice, these values ranged from 0.08 to 0.15 T.U. and from 44.80 to 80.75, respectively. Thus we saw that red-kerneled rice showed a larger variation in physicochemical properties than white-kerneled rice. Milled red-kerneled rice contained more protein and had lower maximum viscosity and breakdown values than white-kerneled rice. Cooked red-kerneled rice had lower adhesion and a higher ratio of hardness / adhesion than white-kerneled rice. The large variation in physicochemical properties of the red-kerneled rice is indicative that the breeding of new rice varieties for special utilization will be possible.

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Using two varieties of wheat with genetically differing leaf lengths, several parameters concerning leaf growth were examined under controlled environmental conditions. Heritabilities for the parameters of leaf growth were calculated based on measurements of F₂ generation of the hybrid between these two varieties. The rate of leaf emergence (i. e., the speed of leaf emergence per unit time or per unit length) was almost the same between the two parent varieties, although the average length of leaf and average number of days required for the emergence of one leaf were different due to the difference in leaf length. Heritabilities for the average length of leaf and for the days required for the emergence of one leaf were 77.7 and 85.2%, respectively. In F₂ generation, however, no correlation was detected between the two characteristics (r=0.152). The heritabilities for the speed of leaf emergence per unit time and unit length were 55.5 and 45.2%, respectively, suggesting that the leaf growth rate (speed of leaf growth per unit time and per unit length) can be changed by selection.

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Using the micropropagated potato shoots of 'Benimaru', 'May Queen', and 'Danshakuimo', originating from a meristem culture, the effects of 2-chloroethyltrimethylammonium chloride (CCC) and benzyladenime (BA) on the formation of microtuber were investigated. The number and fresh weight of microtubers after 28 days of culturing were largest in the Murashige and Skoog (MS) solid medium supplemented with CCC (500 mg L^-1) and BA (5 mg L^-1) under dark conditions. This indicates that the tuberization medium proposed by the International Potato Center (CIP) is available for the formation of microtuber of the three cultivars described above. It was also found that CCC was effective for increasing the number of microtubers at the early stage of culturing, and that the fresh weight of microtuber of 'May Queen' was relatively small as compared to those of the other two cultivars. Scanning electron microscopy (SEM) revealed an external morphology at the stage of transforming into tuber from axillary bud after two days of culturing on a medium supplemented with CCC (500 mg L^-1) and BA (5 mg L^-1) in the dark at 20°C.

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Four field-grown potato cultivars, Irish Cobbler, May Queen, Dejima and Nishiyutaka, were subjected to measurements of leaf nitrate reductase (NR) activity (in vivo assay) and the distribution of nitrogen during growth and development. Varietal differences in NR-activity averaged over a season were observed : Highest activity was Nishiyutaka (6.08 NO₂^- μmol h^-1 g^-1 fresh weight) and lowest was May Queen (4.92 NO₂^- μmol h^-1 g^-1 fresh weight). Slightly high NR-activities were observed during the 30 days of early growth in all cultivars, and as growth proceeded, they tended to fall. The NR-activity was positively correlated with the percentage total leaf nitrogen, and with nitrogen accumulated in the leaf. The NR-activity had no correlation with total dry matter or tuber dry matter. The accumulation of nitrogen in the leaves declined with age, whereas it increased in the tubers regardless of the cultivar. At the end of the season, all cultivars except Nishiyutaka accumulated almost the same level of nitrogen in the tubers. A significant linear correlation (r=0.749***) was found between the natural logarithm of SPAD reading (relative chlorophyll content) and NR. Harvest indices for nitrogen showed that the partitioning of nitrogen to the tubers was higher in Irish Cobbler and May Queen than in Dejima and Nishiyutaka. There was no evidence to conclude that NR-activity has a direct effect on dry matter production in potato.

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Floating rice (Oryza sativa L.) responds to submergence by rapid internodal elongation. This stimulated growth needs an increase in the supply of photoassimilates. We investigated the effects of submergence on the export rate of photoassimilates determined by a 13C-tracer experiment and the activity of sucrose phosphate synthase (SPS), a key enzyme in the sucrose biosynthesis pathway, in floating rice. Plants at the 9.5 leaf stage were submerged up to the tip of the 7th leaf blade for 5 days. Export rates of the ¹³C-photoassimilates at the 9th (9L) and 10th (10L) leaf blades were much higher in the submerged plants than in the control. In order to analyze the activation state of SPS, the activities of SPS were assayed under saturated substrates (Vmax) and limiting substrates plus Pi (Vlimiting) . The Vlimiting of SPS of the 9L and 10L were higher in the submerged plants than in the control, whereas the Vmax did not differ between both plots. These results indicate that the SPS of the leaves in the upper position was more highly activated in the submerged plants. Moreover, the Vlimiting of. SPS was correlated positively with the export rate. These results suggest that an increase in the Vlimiting of SPS induced by a high activation state might accelerate the export rates of photoassimilates, and that this is probably one of the important factors that support the supply of photoassimilates required for the rapid growth of the sink organs in submerged floating rice.

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The acetylcholine (ACh) -acetylcholine receptor system requires the presence of acetylcholinesterase (AChE) and Ca²⁺ as a trigger of ACh release at the plasmodesmatal junction between the stele and cortex in plants. In this work, Ca²⁺ movement and cytochemical AChE activity were detected in the coleoptile node cells of maize seedlings following heat stress. Fluorescent Ca²⁺ labeled with calcium green was detected in the cells with a laser scanning confocal microscope. The labeled Ca²⁺ in the coleoptile node cells was found mainly in starch grains. Heat stress remarkably increased labeled Ca²⁺ in the endodermal and cortical cells. Most of the starch grains in the endodermal cells lost shape immediately after the treatment of heat stress, and the crumbling starch grains exuded labeled Ca²⁺ into the cells. From the results, the Ca²⁺ in starch grains can be activated by heat stress, and consequently, the released Ca²⁺ can induce an elevation of Ca²⁺ concentration in the cells. Further, the endodermal cells rapidly responded to heat stress as compared to the cortical cells. The AChE activity in the endodermal cells also greatly increased after heat stress. Therefore, the appearance of Ca²⁺ in endodermal cells after heat stress can be correlated to its function as a trigger for ACh release.

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The influence of potassium (K) deficiency on leaf water and osmotic potentials, and concentrations of major solutes was determined to assess their contributions to the leaf growth of soybean plants grown in solution cultures containing 5.0 and 0.2 mM KCl. A deficient supply of K restricted leaf growth due to decreased mesophyll cell numbers and cell enlargement, though water content, water and osmotic potentials of the expanding leaves were not affected by the treatment. The osmolarity of the expanding leaves showed very similar values in both treatments, though the K⁺ concentration in the K-deficient plants was remarkably lower than that of the control. In response to the K-deficiency, some cations, anions, sugars and amino acids accumulated in the expanding leaf, compensating the decrease in K concentration approximately 92%. These findings suggest that the leaf growth depression observed in the K-deficient plant occurred when the water relations of the K-deficient leaves are maintained close to that of the control.

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Heterosis, general (GCA) and specific combining ability (SCA), and their effects were studied for six major characters in a diallel mating system in early maturing sorghum by sowing in spring and summer. The GCA and SCA effects were highly significant for all traits studied. Some parents were identified having high positive GCA for grain yield, and low or negative GCA for culm length and days to heading which were considered as good combiners. High positive heterosis in grain yield was found for more than half of the hybrids studied. Several cross combinations had high grain yield heterosis, negative days to heading heterosis, low culm length heterosis and good performance. Genotype×seeding time interaction effect was significant for grain yield, culm length and days to heading. Genotype×planting density interaction effect was significant for grain yield in spring seeding but not in summer seeding. It is suggested that the selection of good genotypes adapted for summer sowing could be applied to either 10 or 20 cm planting densities but must be carried out in summer seeding. Some hybrids were proposed as promising cultivars if sorghum is grown after an early-season rice crop.

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