Rice yellow mottle disease caused by Rice yellow mottle virus (RYMV) is one of the major threats to rice production in Uganda. Host resistance which is considered as the most effective and sustainable control measure is hindered by limited resistant genetic resources. We evaluated the reaction of Ugandan and some foreign rice cultivars against RYMV to select moderately resistant cultivars. To validate the assessment by symptom appearance and ELISA, plants were inoculated at 21 (early inoculation) and 35 (late inoculation) days after sowing (DAS) and evaluated at 28 days post inoculation. A positive relationship between assessment by ELISA value and symptom appearance was observed. Significant differences were observed between the influence of early inoculation and late inoculation. In early inoculations lowland rice cultivars showed higher disease severity than upland cultivars. Early inoculation was suitable for selection of highly resistant cultivars while late inoculation was better in selection of moderately resistant cultivars. Also, wild rice species and some Japanese upland rice cultivars were examined by inoculation at 21 DAS. Overall, using symptom appearance, plant height reduction percentage, ELISA and RT-PCR, 2 foreign rice cultivars and 4 wild rice species were highly resistant and 4 foreign cultivars and 6 Ugandan upland rice cultivars were moderately resistant. All the Ugandan farmer favored cultivars tested in this study were susceptible to RYMV. Cultivars with moderate resistance selected in this study should be introduced alongside the existing sensitive cultivars desired by the farmers.
Improvement of the sugarcane canopy structure using varietal diversity in leaf erectness should effectively increase the number of millable canes, which is highly correlated with cane yield. Traditionally, leaf erectness has been evaluated with visual observations; however, quantitative analyses using leaf morphological features would be a more practical means of selecting optimal leaf erectness. The objective of this study was to develop a new evaluation method using the leaf features to characterize the leaf erectness. Thirty-seven sugarcane genotypes were evaluated by means of leaf silhouette sketches. The correlation between the conventional leaf-erectness scores and the leaf features suggested that the aboveground height of leaf tips best characterizes varietal leaf erectness. Therefore, we developed a leaf erectness index (LEI) as the ratio of leaf tip height to aboveground height of its dewlap. The values of the LEI were useful for characterizing leaf erectness because they significantly correlated with the leaf-erectness score with indices ranging continuously from 0.36 to 2.55. When quantifying LEI at different growth stages and under differing environmental conditions, it is better to compare the measured LEI for a given variety to the LEI of a standard variety.
Perennial water shortage in the downstream area of the Mwea Irrigation Scheme (MIS) remains a major problem. Therefore, some farmers try to increase their cash income by cultivating horticultural crops after the main rice crop, but their cultivation technology has not yet been established. We conducted a field experiment to study the effectiveness of different surface drainage methods and how they affect the yield of selected crops because the vertisol that dominates the irrigated area is highly fertile but has extremely poor drainage. We compared a control area with surrounding ditches with a new drainage area consisting of additional ditches within the field. During the 2016 long rainy season (January–July), the period when soil water tension starts to rise in the new drainage area was earlier than that in the control area. The soil water content in the control area was slightly higher compared to the new drainage area. Therefore, it was found that the drainage capacity was enhanced by the new drainage method. There was no significant increase in the yield of soybean or green gram due to the drainage improvement. Meanwhile, disease occurrence was suppressed and the yield was increased in tomatoes by improving field drainage, and also by using “Rambo F1” and “Kilele F1”. Therefore, it was shown that bacterial wilt resistant cultivars are effective for secondary tomato cropping in MIS paddy fields.
Short photoperiod and high temperature could be causal factors for the low productivity of soybean in tropical Asian countries. In order to find adaptable genotypes suited to tropical areas, we evaluated the variation in responses to photoperiod and temperature of soybean in the world mini-core collections (GmWMC). Seeds were sown in late May (long photoperiod) and early August (short photoperiod) from 2015 to 2017 in the field and in a growth chamber at Saga University, Japan. The dates of emergence, first flowering (R1), first pod appearance (R3), and the start of seed filling (R5) were recorded. The daily average temperatures and photoperiodic hours were collected from weather stations. The days from emergence to first flower open (DEF) were shortened by late sowing in all genotypes, whereas the accumulated temperatures during emergence to first flower open (ATEF) did not respond to sowing time in some early flowering genotypes, indicating that these genotypes may be insensitive to photoperiod. The accumulated temperature (AT) of R1–R3 (for pod formation) responded to the sowing time similarly to that for flowering. However, there were no such responses observed for AT of R3–R5 (for pod elongation). The growth chamber experiment showed a longer DEF at lower temperature; however, the ATEF and EATEF (effective ATEF) did not respond to the change in temperature. The results suggested that ATEF could represent photosensitivity better than DEF in natural conditions, and temperature might affect plant development quantitatively in soybean.
‘Big Sister’ cherimoya was pollinated using pollen from ‘Big Sister’ and ‘Fino de Jete’ cherimoya and ‘Gefner’ and ‘Pink’s Mammoth’ atemoya and the fruit set and quality were evaluated to test the effects of the pollen parent. Cherimoyas showed germination decrease in summer, while atemoyas did not. Cherimoya pollen caused high (80–95%) fruit set in May–June, while the fruit set decreased to 50% in summer, similar trend to germination. Using atemoya pollen resulted in generally low (<60%) fruit set and the fruit set decreased to less than 20% in summer. Atemoya pollen caused decreases in seed set, fruit weight, and symmetricity, although it tended to enlarge the fruit more than in cherimoya for the same seed set. Pollen parent effects were remarkable on cherimoya. ‘Gefner’ pollen tended to produce globose fruit. ‘Fino de Jete’ pollen produced fruit of the highest eating quality. Atemoya pollen tended to decrease eating quality and resulted in a firm flesh texture. The pollen parent did not affect the soluble solid content. Seed morphology differed markedly: self-pollen produced the heaviest and longest seeds, while ‘Fino de Jete’ pollen produced the lightest and smallest ones. Atemoya pollen resulted in thick, globose seeds. Using atemoya pollen decreased cherimoya fruit set and changed the fruit quality more irregular in shape, smaller, and less tasty than using cherimoya pollen.