Conidia aerobiology and cercosporiosis management of soybean (Glycine max) / Aerobiologia de conídios e manejo das cercosporioses da soja (Glycine max)

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

The cercospora leaf blight and the frogeye leaf spot are two important diseases of soybean culture. Due to the high variability of both pathogens, the search for new sources of resistance and for efficient control methods is necessary. Therefore, this work, divided into five chapters, had as general objectives: (a) the evaluation of soybean genotypes reaction to both diseases; (b) the effect of fungicide treatments on control of the diseases; and (c) the monitoring of airborne spores of C. kikuchii. On chapters 1 and 2 the specific objectives were the evaluation of the reaction of soybean genotypes (conventional and transgenic Roundup Ready) to cercospora leaf blight and to frogeye leaf spot, respectively, and the effect of fungicide applications on the diseases in field conditions. For these purposes, seven experiments were conducted during the crop periods of 2005/06, 2006/07 and 2007/08, and a total of 116 genotypes was evaluated. On chapters 3 and 4 the studies had as specific objectives the evaluation of inoculum concentrations, the virulence of isolates and the reaction of soybean genotypes under greenhouse conditions to C. kikuchii and C. sojina, respectively. On chapter 5 the specific objective of the study was the quantification of spores of C. kikuchii and its relation to the disease intensity and to the environmental factors temperature, relative air humidity (RH), precipitation and leaf wetness period in two crop periods. To quantify the airborne conidia, a Burkards seven-day volumetric spore trap and a weather station were set in an experimental field with soybean culture. On chapter 1 there was significant difference among genotype reactions for the variable INC (% of foliar incidence) in the experiments 1 and 2, and for the variables AFL (% of foliar diseased area) and AUDPC (Area under the disease progress curve) in the experiment 7. On experiments 3, 4, 5 and 6 there were no significant differences among the genotypes. The cercospora leaf blight intensity was low on the experiments (AFL 0 to 1.5%), but it is interesting to report that GT04-7439 GT04-8114 (experiments 1 and 4) presented less or did not present any apparent disease symptoms. On chapter 2 there was difference among genotypes in experiment 1 using the variables AFL, INC, NLL (number of lesions by leaf) and AUDPC, and GT04-7470 showed lesser levels of frogeye leaf spot than the other genotypes. In the experiment 2 difference among genotypes was observed in INC and NLL. The genotypes GT04-7310, GT04- 7781, Msoy 8866 (experiment 3) and GT04-7606 (experiment 4) did not show any symptoms. On experiment 6 the genotypes differed among each other using NLL, and Msoy 8787 RR showed the lowest levels of disease. There was no differences among genotypes on experiments 5 and 7. On experiments 3, 4, 6 and 7 the fungicide treatments did not show difference among each other, although the three application treatment (experiment 7) was different from control (no fungicide). The disease intensity in all experiments was considered low (AFL under 1%), which may indicate that the genotypes showed resistance to the frogeye leaf spot. On chapter 3 there was difference among inoculums concentrations, and the 10g of mycelium/100mL was selected. In the virulence assay difference among isolates was verified in AFL and INC (Cerc 211 and Cerc 212 more virulent) when isolates were inoculated in the cultivar Emgopa 313, although all isolates showed some virulence degree. There was difference among the 10 genotypes reactions in the trials 1 and 2 to the isolates inoculated. The AFL variation was of 0,231 to 1,275% and INC variation was of 3,078 to 37,028%. On chapter 4 there was difference between the inoculums concentrations, and it was selected the concentration of 105 conidia/mL. There was significant difference among all C. sojina isolates on the virulence trial on the variables AFL, INC and NLF. The isolates Cerc 214 (race 15), Cerc 210 (race 4) and Cerc 217 (race 24) were the most virulent using the variables AFL, INC and NLF. To evaluate the reaction of genotypes to C. sojina, it was carried out two trials. There was significant difference among genotypes on experiments 1 and 2 to all four variables and on both isolates (Cerc 214 and Cerc 210). Genotype GT04-8901 showed lower levels of the disease and differed significantly from Msoy 8001, which showed more symptoms caused by isolates of races 15 and 4 in both trials. AFL of 10 genotypes was under 1%. On chapter 5 it was verified that most of the conidia were collected during the day, with over 60% of the spores collected between 8 and 15h in both crop periods. Climatic data varied according to the crop period, but in general in both experiments the major collection of spores occurred with reduction of precipitation and leaf wetness period. RH above 80% and temperature between 20 and 24C were more favorable to capture of conidia and disease intensity. In the two years of evaluation the major amount of spores were collected when plant stage was R6-R7, as well as disease intensity increased after beginning of reproductive stage of soybean. Although the number of captured conidia in the 2006/07 crop period was higher than the next year, the variation of fluctuation of spores during culture cicle occurred similarly.

ASSUNTO(S)

fungicida frogeye leaf spot fungicide ciencias biologicas cercospora sojina crestamento foliar resistance cercospora sojina cercospora kikuchii cercospora kikuchii mancha olho-de-rã resistência cercospora leaf blight

ACESSO AO ARTIGO

Documentos Relacionados