The yield of potato (Solanum tuberosum) was evaluated when intercropped with maize (Zea mays) in Nepal. The objective was to study ways of increasing potato yield within the intercrop by altering planting dates and using a fungicide to reduce the incidence of late blight. Two field trials were carried out in 1994 and 1995 at 2200 m a. s. l. Three local potato cultivars, Rato Aalu, Sarkari Seto and Hale were intercropped with the local maize cultivar Seti Makai. Both trials tested the planting times of local potato cultivars. The effect of chemical control of late blight infection was also monitored in 1995.
Results for time of planting suggested that the potato cultivars Ratu Aalu, Sakari Seto and Hale gave higher yields when planted early, medium, and late respectively, as followed by local smallholders. Fungicide spraying against blight led to potato tuber yields of up to 19 t/ha for sole crops and slightly lower increases for intercrops but all in excess of unsprayed treatments. Maize yields were not affected by the enhanced potato performance. For both experiments intercropping resulted in yield improvements with LERs (Land Equivalent Ratios) ranging from 0.93 to 1.89. It is concluded that intercropped potato cultivars could achieve short-term tuber yield increases. The sustainability of such yield increases are discussed.

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A field experiment was conducted in 1997 to study the uptake and distribution of ¹⁵N-labelled ammonium sulfate fertilizer by maize under the humid tropical conditions of Malaysia. The soil was classified as Bungor series (Typic Paleudult) with a sandy clay loam texture. The recommended N rate applied was 150 kg N⋅ha_-1in the form of (NH₄) ₂SO₄, of which 60 kg N⋅ha^-1 was applied as (¹⁵NH₄) ₂SO₄, (9.82 atom percent ¹⁵N excess) . At harvest, the percent of nitrogen derived from labelled fertilizer (%Ndff) in the above ground plant parts was 23.0 %. The total recovery of applied fertilizer ¹⁵N was only 20.4 %. More than 60% of the fertilizer ¹⁵N recovery was found in the stover (stalks and leaves), 11.6 % in the husks, 3.0 % in the empty cobs and 23.7 % in the grains. Total ¹⁵N recovery in the top 50 cm soil was 39.6 %, of which 74.5 % was found in the 15 cm topsoil. The amount of total labelled N unaccounted for was 40 %. The main channel of ¹⁵N loss was presumably leaching.

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To clarify the process of chilling injury, this study was undertaken to determine the chlorophyll fluorescence and the enzyme activity for scavenging of free radicals in banana fruits kept at chilling temperatures as well as fruit physiological changes. Banana fruits (cv. Cavendish) at the mature green stage were stored at 5, 13 and 20°C, respectively, for comparative studies. The results showed that the fruits stored at 20 and 13 °C reached the ripening stage after 2 and 3 weeks of storage, respectively, based on the rapid increase in the respiration and ethylene evolution rates, color change, firmness of peel and pulp, and chlorophyll fluorescence. In contrast, fruits stored at 5 °C showed slightly higher respiration and ethylene evolution rates, and a marked increase of CO₂ production when transferred to 20°C after 2 weeks of storage, indicating the presence of chilling injury symptoms. The Fv/Fm ratio of the fruits stored at 5°C for 2 weeks was lower than that of the fruits stored at 13 and 20°C. In addition, chlorophyll fluorescence measurement could be used to predict the occurrence of chilling injury for banana fruits as a non-destructive method of measurement before tissue damage becomes visible. SOD, catalase and peroxidase activities of the fruits stored at 5°C and subsequently transferred to 20°C were higher than those of the fruits stored at 13 and 20°C, respectively, when chilling injury symptoms occurred.

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Rice (Oryza sativa L.) yield is low under saline soil conditions due to the small number of spikelets per panicle (SN) and there are varietal differences in the sensitivity of SN to soil salinity. This study was carried out to determine whether varietal differences in the sensitivity were attributable to dry matter production under saline soil conditions. A sensitive variety IR28 and a tolerant variety IR4595-4-1-13 were grown in pots filled with sand and submerged in four saline solutions containing 25mM to 150mM sodium chloride (NaCl) from the later stage of spikelet initiation to the panicle emergence stage and compared to plants grown under low solar radiation (30% to 80% of natural radiation) . Control plants were grown without NaCl application under natural solar radiation. Under the saline conditions dry matter increase per shoot (ΔW) was more reduced in IR28 than in IR4595-4-1-13. The percentage of decrease of SN in IR28 was larger than that in IR4595-4-1-13, where the degeneration of spikelets on secondary rachis-branches was the main cause of the decrease of SN. The panicle dry weight at panicle emergence (Wp) was related to SN and the decrease of ΔW was responsible for the small Wp since dry matter distribution to the panicle (Wp/ΔW) did not change. There was almost no accumulation of sodium in panicle, but substantial accumulation was observed in leaf and stem, IR28 being a better accumulator. Under the low solar radiation conditions, though IR4595-4-1-13 maintained higher SN, there were small varietal differences in the response of ΔW, Wp and SN, while Wp/ΔW was enhanced due to the low solar radiation. Therefore, IR4595-4-1-13 was tolerant in terms of SN to soil salinity because a lower sodium concentration in leaves may maintain dry matter production, thus the limited changes in ΔW and Wp, resulting in a limited change in SN.

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Through successive backcrosses, the cytoplasm and nuclear fertility restorer gene of K98, a line of Oryza rufipogon, were introduced into Taichung 65, O. sativa, and a nuclear-substituted line, RT98C, was developed. This line showed a high degree of spikelet fertility, but it produced fertile and sterile plants in the cross with Taichung 65. To analyze the mode of inheritance of the fertility, crossing tests were carried out, and the following results were obtained.
Pollen fertility was controlled by the interaction of the cytoplasm and the single restorer fertility gene (Rf-rf), but the function of the embryosac was not affected by the cytoplasm and restorer fertility gene. That is, all the pollen grains in the cytoplasm of Taichung 65 were normal regardless of the dominance or recessiveness of the restorer fertility gene they carried. On the other hand, the pollen grains carrying the Rf gene in the cytoplasm of RT98C were normal, while the pollen grains carrying the rf gene in this cytoplasm became sterile. The normal cytoplasm of Taichung 65 was designated as (mfc) and the sterile cytoplasm of RT98C as (msc) .
When the (msc) Rfrf plants were selfed, in all the resulting plants, spikelet fertility was restored, and no sterile plants were observed, suggesting that the pollen grains carrying the rf gene were not viable. Thus, the male sterility and fertility restoration in this line were controlled by the genotype of the gamete itself but not by that of the zygote, indicating the presence of a gametophytic control of fertility.
Only in the (msc) rfrf plants spikelet fertility was not restored, while in the plants with all the other genotypes, viz. (msc) RfRf, (msc) Rfrf (mfc) RfRf (mfc) Rfrf and (mfc) rfrf spikelet fertility was restored, resulting in a high degree of spikelet fertility. Although pollen grains carrying rf in (msc) degenerated regardless of the plant genotype (Rfrf or rfrf), they all stained well in a I₂KI solution and showed a normal size.

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The effects of the concentrations of two kinds of sugars on nodal segment culture were investigated using two varieties of D. alata, Africa and Okinawa-A. Nodal segments of the two varieties were cultured on solid MS medium supplemented with 2, 3, 4, 6 and 8 % of sucrose or glucose at 25°C under a 16/8 hr day/night photoperiod.
The kinds and concentrations of sugars did not affect appreciably the regeneration rate but exerted a considerable effect on the top and root dry weight of the regenerated plantlets in both varieties. Sucrose appeared to be more effective to increase the dry weight of the top and roots of the regenerated plantlets than glucose. For cv. Africa, the dry weight of the top and roots markedly increased at a sugar concentration above 6 %. For cv. Okinawa-A, the increase of the top dry weight was promoted at higher concentrations of sucrose, while the growth response to the changes in the glucose concentrations was limited.
It is concluded that higher concentrations of sugar are more effective for nodal segment culture of D. alata.

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By setting up three development phases in irrigated agriculture in relation to the development of farmland, i.e., land opening, irrigation new construction and irrigation rehabilitation/modernization, and by using the data compiled for the last half century since independence in the Philippines, we conducted cost-benefit analyses and showed that the crop sector in the Philippines passed through the first two phases, and reached the last phase by 1990. It was observed that government irrigation investment, while restricted by the long-run needs of the sector, has been subjected to wide shortrun fluctuations. In the present phase, investment for the rehabilitation and maintenance of irrigation system, in particular, has been insufficient, in spite of the high rates of return to such investment. To achieve agricultural development in this phase, it is necessary to address these issues.

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