Ratoon stunting disease: severity of xylem symptoms and quantification of field and industrial damages

Um experimento de blocos ao acaso com parcelas sub -divididas e 6 repetições com 10 variedades de cana-de-açúcar tratadas termicamente (TT) e inoculadas (RS) foi desenvolvido na região de Piracicaba-SP. Através do Método de Coloração do Xilema pelo fluxo transpiratório (CXFT) as variedades foram avaliadas em relação: a) severidade do RS no Xilema b) resistência a evolução da doença c) tolerância à ação da bactéria do RS d) danos agro-industriais em função do ISRS%. Os resultados demonstraram que as variedades diferiram em relação à severidade da doença. Sendo a RB785148, RB805246 e SP70-1143 resistentes; CP44-101, RB72454, RB785343, RB806043, SP70-1284 e SP79-1011 intermediárias e a NA56-79 suscetível. A CP44-101, RB72454, RB785343, RB806043, SP70-1284 e SP79-1011 foram tolerantes à ação da bactéria. A RB785148 e SP70-1143 intermediárias e NA56-79 e RB805246 intolerantes. A quantificação do ISRS% do Xilema e a estimativa de danos agro-industriais entre colmos TT e RS permitem a seleção de variedades resistente (tolerante e intolerante) intermediária (tolerante e intolerante) suscetível (tolerante e intolerante) e a elaboração de modelos de regressão linear para estimar danos agro-industriais de canaviais comerciais em função do índice de severidade do raquitismo da soqueira (ISR 5%)The absence of symptoms characteristic of ratoon stunting disease (RSD) and the lack of specific methods to quantily xylem disease severity have made the detection of the disease and the quantification of the agro-industrial damage in nurseries and commercial fields difficult. Therefore, the present study proposed to: a) evaluate quantitatively the severity of RSD in obstructing xylem vessels; b) evaluate the resistance of sugarcane varieties to the evolution of the disease; e) evaluate the tolerance of sugarcane varieties to the action of RSD bacteria in the stalk; and d) estimate the agro-industrial damage resulting from the severity index of ratoon stunting disease (SIRS%), by using the stainning of xylem vessels by transpiratory flow (SXTF) method. A experiment was set up which 10 sugarcane varieties submitted to long hot water treatment (LHWT) or inoculated (RSD) in a randomized block and split plot design and 6 replications. The results showed that the behavior of the varieties was similar, whether treated with hot water or inoculated with RSD. However, there were differences in the percentages of xylem vessels stained. Ten varieties were evaluated with regard to RSD incidence, where RB785148, RB805246 and SP70-1143 proved to be the most resistant to initial infection; CP44-101, RB72454, RB785343, RB806043, SP70-1284 and SP79-1011 showed intermediate resistance, whereas NA56-79 was the most susceptible. Varieties RB785148 and RB805246 were the most resistant to the evolution of the disease after plant cane harvesting, wile CP44-101, RB72454, RB806043, SP70-l 143, SP70-1284 and SP79-101 l showed intermediate resistance, and the most susceptible were NA56-79 and RB785343. ln terms of xylem SlSR3â4, in plant cane, varieties CP44-101, RB72454, RB785343, RB806043, SP70-1284 and SP79-1011 were the most tolerant; NA56-79, RB785148 and SP70-l 143 reacted as intermediate, while RB805246 proved to be intolerant to the bacteria in the stalk. ln ratoon cane, variety NA56-79 apparently reached its maximum disease threshold, showing high yield damage and proving to be the most intolerant, while the other varieties under study were tolerant to the bacteria action, regardless of the disease index presented. The quantification of ratoon stunting severity of the xylem and estimates of agro-industrial lasses between hot water treated and RSD stalks, permits the selection of resistante (tolerant and intolerant), intermediate (tolerant and intolerant) and susceptible (tolerant and intolerant) varieties in breeding programs and the development of linear regression models to estimate yield damages in nurseries and commercial fields as a function of the disease inde