Drought Tolerant Index and Heterosis Level of Soybean {Glycine max (L.) Merrill} Genotypes

Drought stress on soybean crops in some areas becomes more severe due to climate change. The objective of this study was to estimate the drought stress tolerant index (STI) and heterosis level of soybean genotypes derived from crosses of Grobogan (G) and Dering 1 (D) varieties. Field research was conducted in Probolinggo, East Java, Indonesia, during late dry season of 2016. A total of 17 soybean genotypes consisted of 15 lines derived from crosses of G x D varieties, and two check varieties (Grobogan and Dering 1) were tested using a randomized block design and repeated three times. Each genotype was grown in two environments, namely, optimal irrigation condition (irrigation applied in planting until ripening pods) and drought condition in the reproductive phase (irrigation applied in planting until flowering). Results of the study showed that in drought condition, line (G/D) -99-32-14 had the highest seed weight/plant, highest STI, and highest both heterosis and heterobeltiosis value base on seed weight/plant. In drought condition, most of the soybean lines showed positive heterosis values on 100 seed weight. The cross of Dering 1 and Grobogan varieties produced one soybean line (G/D) -99-32-14 which was more tolerant to drought and had seed size (100 seed weight) higher than Dering 1 (the current drought tolerance variety). It is concluded that it is possible to obtain soybean genotype tolerant to drought having higher seed yield and medium seed size than the better parent.