Biochemical, physiological and epidemiological characterization of soybean genotypes (Glycine max) with partial resistance against soybean rust (Phakopsora pachyrhizi Sydow & P. Sydow)

Abstract

Climatic conditions, inoculum concentration, and plant susceptibility directly affect the manifestation of Asian rust in soybean also plant resistance is characterized by an alteration in pathogen survival skills and perpetuation process. The development of new resistant cultivars against diseases is a primordial step in the preservation of plant yield since the chemical control is losing efficacy in field. The objective of this work was to analyze a diversity of parameters, interacting with a commercial cultivar and soybean genotypes with partial resistance in Asian rust management, under different conditions. In the first study we identified the reaction and interaction of a single fungicide spray with 6 soybean genotypes and one susceptible standard (Desafio RR 8473 RSF) of the soybean breeding and improvement program developed by (LAGER / UFU), after inoculation of Phakopsora pachyrhizi. The variables evaluated made before and after inoculation, consisted on agronomic traits and disease progress. The study was conducted in two different seasons inside a greenhouse. The results indicated significant difference between season and genotype and interaction between split-plots (p<0.05). The Genotypes 2 (F8 BRSGO Luziânia X Potenza), 3 (F8 BRSGO Caiapônia X Potenza), 6 (F8 BRSGO Luziânia X Potenza) performed partial resistance, so we can conclude that exist genes of interest in the Brazilian germplasm, cultivar Potenza. In the second paper, the objective was to evaluate the activity of enzymes (POX and PAL), formation of horizontal barriers and photosynthetic parameters in plants infected with Asian rust. The genotypes that stood out with the higher overall enzyme activity (PAL, POX), lignin content and epidermis cell wall thickness was the 2 (F8 BRSGO Luziânia X Potenza) and 3 (F8 BRSGO Caiapônia X Potenza), these genotypes showed chemical traits for horizontal resistance composition. In the third experiment, the influence of temperature (18, 21, 24, 27 and 30 °C) and leaf wetness duration (0, 6, 12, 24 and 48 hours) on the penetration of the causal agent of soybean Asian rust (Phakopsora pachyrhizi) was quantified under controlled environment. There is a relationship between temperature, leaf wetness with AUDPC and incubation period. The highest AUDPC occurred at 24 °C and leaf wetting period of 24 hours, however the highest AUDPC were in the range of 21 to 24 °C of temperature and after 12 hours of leaf wetting duration. The genotypes 2 (F8 BRSGO Luziânia X Potenza) and 3 (F8 BRSGO Caiapônia X Potenza), showed partial resistance traits against rust progression, during the monocycle experiment.