Genotypic and phenotypic variation among 16 isolates of Ramularia areola of Gossypium hirsutum collected from five different geographical regions of Brazil was studied through virulence spectrum on three cultivars in the glasshouse and through ERIC-and REP-PCR and ITS1-5.8S-ITS2 rDNA analysis. Difference in virulence spectrum and molecular analysis of some isolates was observed. ERIC-and REP-PCR showed similar results and revealed a high level of diversity among the isolates. A unique profile for both ERIC and REP was obtained for most isolates. On the other hand, the ITS rDNA analysis did not show different PCR-RFLP patterns. While some isolates differed among each other considering genotypic and phenotypic reactions, no clear cut evidence was found about the existence of genetic lineages of R. areola in Brazil. Identification of genetic variability among the R. areola isolates originated from different geographic regions would permit screening of Brazilian germplasm and achieve sources with a wide spectrum of resistance. This is the first report of the genotypic and phenotypic variability among the R. areola isolates originated from five cotton growing regions of Brazil.

In recent years, Corynespora leaf blight is on the increase in cotton and has become an important disease in the State of Mato Grosso, Brazil. It attacks several plant species including soybean. It is not yet known whether the same strain of this pathogen attacks both the crops. The objectives of the present investigation were to verify the genotypic and phenotypic variation between the isolates attacking cotton and soybean and to verify the sources of resistance in cotton. Differential response of 23 cotton genotypes was studied under glasshouse conditions using mixture of two randomly selected isolates of C. cassiicola of cotton in equal proportion. Genotypic variation among three cotton and two soybean isolates was studied using ERIC/REP-PCR and rDNA molecular techniques. With one exception, all the cotton genotypes tested so far were susceptible to C. cassiicola isolates of both cotton and soybean. Similarly, results of both molecular techniques indicated that the C. cassiicola isolates attacking cotton and soybean belong to the same strain of the pathogen in Brazil. Since Corynespora blight is a newly immerging disease of cotton and soybean in Brazil, integration of crop rotation and the sanitary practices are suggested to manage the disease.

Spore production of Ramularia areola has always been a difficult task. Brazilian isolates of R. areola produce spores of variable size and shape. The typical spores are 3 septate, rarely 4 and 5 septate, together with abundant single celled oblong to round bodies-a phenomenon not reported earlier for R. areola. Budding of spores is a continuous process as observed in our isolates. By repeated culturing the pathogen either ceases to produce typical spores or loses its pathogenic character. To solve this problem, a technique was developed to produce large quantity of typical spores under laboratory conditions. Sporulating cultures produced on Petri plates containing V8 juice-agar were kept on the laboratory bench till they became dry and then stored at 5˚C for reisolation and/or for production of fresh inoculum. In such dried cultures spores remain viable for a period of over 12 months, and hence isolates of R. areola originated from different geographic regions can be maintained in sporulating form. Results of the present investigation would aid cotton breeders and pathologists in screening germplasm resistant to Ramularia and in other genetical studies under glasshouse conditions.

Shale water as a by-product obtained by Petrobras, Brazil, during the process of extraction of petroleum from fossil rock may act as an inducer of Systemic Acquired Resistance (SAR) to some plant pathogens. The objective of the present investigation was to verify the effect of seed treatment and foliar application with shale water in inducing SAR of soybean to soybean rust under greenhouse and field conditions. In greenhouse experiments, seed treatment alone with shale water significantly reduced the severity of soybean rust and the control efficiency after 11 and 14 days after inoculation was between 54.1% and 57.8%. Whereas seed treatment and only one foliar application with shale water the control efficiency due to SAR 14 and 11 days after inoculation was between 99.7% and 100%, respectively. Such treatments gave similar results under field experiments where the control efficiency of soybean rust was between 79.0% and 99.35% in shale water treated plots as compared to the untreated plots, in 2015. Consequently, this resulted in yield increase between 14.8% and 28.8% depending upon the seed treatment and foliar applications with shale water alone or in mixture with a fungicide. Seed health testing revealed lower number of seeds infected with some pathogens in treatments where either shale water or fungicide was used. Seed treatment and one foliar application were sufficient to induce SAR against soybean rust. This is the first report to demonstrate SAR of soybean to soybean rust induced by shale water. Patent regarding this investigation is deposited with Petrobras, Brazil, under the number EVP 14/022.

RESUMO A pústula bacteriana, causada pela bactéria Xanthomonas axonopodis pv. glycines, é considerada uma das mais sérias doenças bacterianas na cultura da soja. O objetivo deste trabalho foi desenvolver e validar uma escala diagramática para a avaliação da severidade da pústula bacteriana em soja. Para a elaboração da escala, foram coletados folíolos de soja com diferentes níveis de severidade, determinando assim os valores máximos e mínimos de quantidade de doença, e os níveis intermediários de severidade da escala foram estabelecidos de acordo com a lei do estímulo visual de Weber-Fechner. Os valores propostos para a escala foram: 1,4%; 3%; 6%; 9%; 20% e 29,5%. Para validação da escala, oito avaliadores, sem experiência na avaliação da doença, avaliaram 39 fotos com diferentes níveis de severidade, sem e com o auxílio da escala. Os resultados das severidades estimadas pelos avaliadores foram relacionados com os valores das severidades reais (determinadas com o software Assess 2.0 a partir de imagens digitais das folhas com sintomas) e submetidos a regressões lineares simples para avaliar a acurácia dos avaliadores. A precisão dos avaliadores foi determinada através dos coeficientes de determinação e da variância dos erros absolutos. As estimativas com o uso da escala diagramática proposta determinaram um aumento significativo do coeficiente de determinação e uma menor variância dos erros absolutos, proporcionando maior precisão e acurácia das avaliações, podendo ser adotada para a avaliação da severidade da pústula bacteriana em soja.