Search Advances on Resistance to Soybean Diseases Caused by Diaporthe-Phomopsis Complex: A Sustainable Strategy to Obtain Safe Food Products

Abstract

Diaporthe/Phomopsis (DP) is a fungal complex, hemi-biotroph that affects more than 900 hosts including cultivated and uncultivated species, native forests, fruits and weeds; they can also survive in seeds and stubble. The pathogenic plasticity of DP has been transmitted by seeds and expanded to different agroecosystems causing the inoculum to introduce a primary infection in disease-free batches of Argentina and diverse regions of the world. This situation prompted the necessity to characterize the pathogenic variability of Dp in the soybean-producing area of Argentina as a first step in developing effective strategies for incorporating Soybean Stem Canker (SSC) and Soybean Stem Blight (SSB) resistance into soybean germplasm. Collection of Diaporthe/Phomopsis isolates from different agro-environments has achieved some advances, such as: i) morphological determination and the first molecular validation into the identity of this fungal complex in Argentina, ii) detection and report that D. phaseolorum var. meridionalis (Dpm) and D. phaseolorum var. caulivora (Dpc) coexistence in the soybean producing area (32 to 34° SL), and iii) detection of variability in the virulence of different isolates of Dpm and Dpc when interacting with soybean genotypes carrying different resistance genes to SSC. This information explained the pathogenic results obtained, which showed that the soybean resistance genes that were effective against Dpm, were not for var. caulivora isolates [1]. To the four resistance genes to CTS-Dpm that were identified in soybean germplasm (Rdm1-4), a new gene was later determined as Rdm5 [2]. On the other hand, a major resistance gene of simple Mendelian inheritance to SSC-Dpc, named Rdc1, was detected and identified by classic genetic improvement and molecular assistance [3]; without discarding the possibility of another gene or genes that are associated with the assayed ones, which could of contributed to the resistance to SSC in soybean [4]. Respect to the Soybean Stem Blight (SSB) disease, caused by P. longicolla (Plo), it was possible to determine the first SSB resistance gene (Rpsb1) to SSB, carried by one of the resistant genotypes, without ruling out the possibility of carrying another associated genes [5]. These advances provide understanding about the effectiveness of the strategies applied and perspectives of plant improvement aimed at incorporating resistance to diseases in soybean.