SEVERIDADE E AGRESSIVIDADE DE ISOLADOS DE Colletotrichum spp. ORIUNDOS DA SOJA

Abstract

Soybean is an important commodity produced in Brazil, with the Cerrado biome as a major producing ecosystem. In the 2021/22 crop 40,950.6 thousand ha were sown with a production of 124,047.8 thousand t. The objective of this work was to evaluate the aggressiveness and actual severity of Colletotrichum sp. isolates on soybean leaves. From 18 isolates (17 isolates plus the control) of Colletotrichum spp. from soybean (majority), coffee, sugar cane, passion fruit, strawberry, chayote, mango and rubber tree, collected in Urutaí (GO), Cristalina (GO), Pires do Rio (GO), Brasília (DF), Vianópolis (GO) and Passo Fundo (RS) were inoculated (mycelium discs) on the center of leaves (with wound) of soybean cv. Guaia 7487RR. The wet chamber experiment, conducted in an entirely randomized design, consisted of 18 treatments, eight repetitions (leaflets). Colony diameter (mm) was evaluated daily for seven days and photographs at seven days were taken for computational analysis of the actual severity. From the measurements of the response variables (lesion diameter, mm) disease progress curves were constructed, the area under the disease progress curve (AACPD), the infection rate (IT) were calculated, and the actual severity was measured. No lesion development was observed in the treatment where only dextrose-agar potato discs were inoculated without the presence of the phytopathogen. The most aggressive isolate was isolate IF 1 [IF 155, Colletotrichum truncatum, soybean, Urutaí, GO] and IF 04 [IF 267, C. truncatum, soybean, Passo Fundo, RS], differing statistically from the others. From the third day on, the latency period was observed for most isolates. The least aggressive isolates on soybean leaves were IF 25 (passion fruit), IF 23 (chayote), IF 14 (Fusarium sp.) and IF 104 (mango), thus confirming some level of pathogenic specialization of the soybean isolates that caused the greatest amount of disease. After the seven days of incubation, isolates IF 1 (Colletotrichum truncatum, soybean), IF 4 (C. truncatum, soybean), and IF 5 (C. truncatum, soybean) showed the highest actual severity (mm2), as measured by digital images. The isolates IF 13 (C. truncatum, soybean), IF 80 (Colletotrichum sp., chayote), IF 104 (Colletotrichum sp., mango), and IF 141 (Colletotrichum sp., rubber tree), were the ones that presented the lowest pathogenicity rate derived from smaller lesion area at the end of seven days of incubation