No abstract

The brown planthopper (BPH) resistance gene bph4 has previously been assigned on the short arm of rice chromosome 6. However, the map position of the gene could not be determined. To detect the bph4 locus, 15 polymorphic simple sequence repeat (SSR) markers covering genetic distance of 0.0-63.4 cM on chromosome 6 were used to survey 15 BPH resistant (R) and susceptible (S) individuals from each of the 95 and 78 F 2 populations derived from crosses of TN1/Babawee and Babawee/KDML105, respectively. One SSR marker, RM586, was associated with the R and S from the F 2 populations. Additional markers surrounding the RM586 locus were examined to define the location of bph4. From the genetic linkage map and QTL analysis of 95 and 78 F 2 individuals, the bph4 locus was mapped at the same chromosomal region of Bph3 between two flanking markers RM589 and RM586. Markers linked to the resistance gene explained 58.8-70.1% of the phenotypic variations and can be used for marker-assisted selection in BPH-resistant breeding programs. In addition, our experiment provides evidence that a recessive gene could behave as a dominant gene under different genetic backgrounds.

Rice technologies that are designed to reduce risks due to climate variations, improve productivity, or overcome labor scarcity are important in tropical Asia. The objective of this study was to evaluate mechanized options for dry direct-seeding of rice in terms of the productivity and production costs in rainfed lowlands. In a series of on-farm research trials over 3 years in Ubon Ratchathani province, Thailand, we compared seeding by seed drills mounted on two-wheel tractors with manual broadcast seeding. Demonstration trials of seed drills and site-specific nutrient management in 2017 with 11 of 26 participating farmers produced 2.50 t ha −1 of grain yield, but unexpected heavy storms forced the other 15 farmers to switch from dry to wet direct-seeding or manual transplanting. The seed drills produced 32% higher grain yield than manual broadcast seeding (3.3 vs. 2.5 t ha −1) in 2014, and 14-24% higher yield (3.3-3.6 vs. 2.9 t ha −1) in 2015. Mechanized seeding enabled seeding rate reduction by 50% in 2014 and by 52-61% in 2015, resulting in lower production costs than with manual seeding. Our results suggest that mechanized dry direct-seeding of rice with improved nutrient management can enhance farmer livelihoods in rainfed environments in northeastern Thailand. This approach can significantly reduce production costs compared with manual transplanting, while maintaining or increasing productivity compared with conventional manual broadcast seeding.

In Thailand, rice production accounts for the largest proportion of irrigated crop production, especially in the dry season. Water shortage problems have recently become widespread in Thailand, with implications for irrigated rice cultivation. Compared with the continuous flooding (CF) technique, the alternate wetting and drying (AWD) technique can reduce the amount of water typically needed in rice systems and can reduce methane emissions produced from paddy fields. In this study, AWD (10/-10, 10/-15, and 10/-20) and CF combined with the broadcasting technique were studied at seven rice research stations in the dry seasons of 2014 and 2015. The results showed that the AWD technique reduced grain yields compared with those of CF, but the milling quality was not significantly different among the treatments. In addition, the total CH 4 emissions from the AWD treatments were less than those from CF, but the percentage of CH 4 reduction in the AWD treatments was different among the seven stations. However, the total N 2 O emissions were not significantly different between the CF and AWD treatments. Thus, if water scarcity is happening and if it is necessary to grow rice in those cases, the AWD10/-10 technique is recommended in broadcast rice systems in Thailand.