Screening and utilization of soybean (Glycine max (L.) Merr.) genotypes for improving resistance against rust

Abstract

Soybean rust is a highly devastating disease, yield losses can range from 13 to 70% [1]. The disease is caused by Phakopsora pachyrhizi [2]. The host range includes soybean (Glycine max (L) Merr.), other Glycine species and a number of genera in the legume family [3, 4]. Four independent single dominant genes conferring resistance to four specific races of the soybean rust pathogen have been identified. The inheritance of resistance in PI 200492, PI 230970 and PI 462312 was studied [5]. The study concluded that each of these genotypes carried a single dominant allele at a different locus conferring resistance to specific rust isolates. The genotypes for rust reaction assigned to the three parental types were PI 200492-Rpp1 Rpp2 rpp2 rpp2 rpp3 rpp3, PI 230970-rpp1 rpp1 Rpp2Rpp2 rpp3rpp3 and PI 462312-rpp1rpp1 rpp2rpp1 Rpp3Rpp3. A fourth major gene conferring resistance to soybean rust was reported in PI 459025 [6]. The study showed that PI 459025 carried a single dominant gene for resistance to all the three rust isolates and that this gene was at a different locus from the three previously identified genes conferring resistance to specific rust isolates. The genotype assigned for rust resistance of PI 459025 is rpp1 rpp1 rpp2rpp2 rpp3rpp3 Rpp4Rpp4. In India, the disease was first noticed in 1970 [7], but became economically important only after its reappearance in 1994 [8]. Barring four varieties, all other Indian varieties were found to be susceptible. Soybean rust has not occurred in an epidemic form in major soybean growing areas of India since last two decades, so race analysis has not been done. Therefore, there is a need to initiate work on various isolates, infection types and physiological races of rust in India [8].