Assessing the effect of resistant-susceptible associations and determining thresholds for associations in suppressing leaf and neck blast of rice

Blast has become a major problem in the upland rice of Indonesia, as the improved resistant varieties with high yield performances released in the 90's became susceptible only a few years after their release. The present study investigated the efficiency of association of susceptible and resistant varieties in reducing leaf and neck blast and increasing yield. Two sets of experiments were conducted in fields with associations through using different proportions of resistant variety, and two types of susceptible variety (moderately and very susceptible) in the association. The efficiency of the association was measured by comparing disease intensity and yield in the variety when grown in association and when grown as a pure stand. ANOVAs and logistic regressions indicated that resistant-susceptible variety association was more efficient in reducing neck blast than leaf blast. Associations were more efficient (1) when the proportion of resistant variety was increased, (2) when a moderately susceptible variety was used instead of a very susceptible variety, and (3) when disease level in the pure stand was higher. Associations did not penalize the performances of the resistant variety, neither in terms of disease intensity, nor yield. Logistic regressions allowed to estimate the probability of a given association to reduce disease (or to increase yield) above a preset threshold, according to the proportion of resistant variety and to the type of susceptible variety.     

A New Approach to Select Doubled Haploid Rice Lines under Salinity Stress Using Indirect Selection Index

This study determined the indirect selection index of doubled haploid(DH) rice using a multivariate analysis approach to select lines adaptive to salinity stress, comprising three experiments. The first experiment involved the selection of good agronomic characters in a field experiment conducted at an experimental station in Bogor, Indonesia. The second experiment involved salinity tolerance screening through hydroponic cultures using 0 and 120 mmol/L NaCl, conducted at a greenhouse in Bogor. The third experiment involved the validation of the indirect adaptability selection index(IASI) through a field experiment in Sukra(saline area). Field experiments followed a randomized complete block design(RCBD), whereas an RCBD nested factorial design was used for the greenhouse experiment. The first and second experiments used 56 DH lines and four check varieties with three replications. In the second experiment, Pokkali and IR29 varieties were also added as tolerant and sensitive checks of salinity, respectively. The third experiment used 28 selected DH lines, Inpari 29 and one sensitive DH line. The good agronomic index(GAI) was 0.465 yield + 0.433 number of productive tillers + 0.31 number of filled grains. This generated 24 DH rice lines with good agronomic traits. The salinity tolerance index(SaTI) was developed through the average of standardized salinity tolerance score and salinity selection index based on discriminant analysis. This generated 34 DH rice lines with good salinity stress tolerance. The IASI(IASI = GAI – Sa TI) selected 28 DH rice lines adaptive to salinity stress and it was considered effective by Sukra validation.     

Nutrient culture media with agar is effective for early and rapid screening of iron toxicity tolerance in rice

The breeding for iron toxicity tolerant rice needs an effective, efficient, and reliable screening method. The study was aimed to evaluate the best method for screening iron tolerant genotypes at the seedling stage in the greenhouse. Two rice genotypes, Mahsuri (tolerant) and IR64 (sensitive) were grown in three modified media solutions namely, Yoshida-conventional solution (YCS), Yoshida with etylenediamintetraacetic acid (1:2) (YES), and Yoshida with 0.2% agar (YAS). Three levels of iron were tested to observe the severity of their leaf bronzing score (LBS). The optimized solution in the greenhouse was then evaluated using 24 rice genotypes. Using the same genotypes interrelationship, the LBS in the greenhouse with grain yield and its attributes was validated under acute and moderate Fe toxicity in the field. The results showed that the optimized media culture was YAS with 400 mg L^-1 of FeSO₄. This media had more stable pH and redox potential, it could maintain sufficient Fe²⁺ supply over 10 days, and it could discriminate of LBS between tolerant and sensitive genotypes. Evaluation using the optimized media solution showed that there was a significant variation among genotypes in shoot dry weight and a significant correlation of relative reduction of shoot dry weight with LBS. The LBS in the greenhouse was correlated with LBS in acute iron stress in the field (r=0.673**) and the grain yield (r= -0.618**). This study has proven that YAS culture media can be used as early identification of iron toxicity tolerant genotypes for supporting breeding programs.