Z. J. M. Cordeiro

Expressão da resistência de variedades de banana à Sigatoka-amarela

Yellow Sigatoka, caused by Mycosphaerella musicola / Pseudocercospora musae continues to be a great problem for the banana (Musa spp.) crop in Brazil, with the causal agent presenting high pathogenic variability among the isolates of the pathogen. The objective of this work was to characterize the reaction type that has been observed among the resistant varieties. The researches have been carried out under greenhouse conditions with artificial inoculation of different isolates of M. musicola on a group of banana varieties, composed by Pacovan, Prata Ana, Thap Maeo, Caipira, Grand Naine, Terra and Pioneira. In inoculations on those varieties, involving about 38 isolates M. musicola, until now only the Terra variety, had its resistance mechanism overcome by some of the isolates. Some of these isolates were also inoculated on other genotypes not included in this relationship, such as: JV03-15, PV03-44, FHIA-01 and FHIA-18. Observing the reactions of the varieties Caipira, Thap Maeo, Pioneira, Terra, JV03-15 and PV03-44, varieties which are resistant to most of the isolates, a very similar behavior is noticed. All of them showed a reaction to powdered inoculation by the formation of barely perceptible lesions shaped like points or grooves. This reaction is similar to a hypersensitive reaction with the formation of local lesions of late visualization. The phenotypes have the characteristics of a qualitative answer, involving a hipersensibility mechanism.

Avaliação de genótipos tetraploides de bananeira cultivados em área infestada pelo agente causal do mal-do-Panamá

ABSTRACT – Fusarium wilt is one of the major diseases which cause great damage to the banana crop in Brazil since most cultivars used are susceptible. This study was carried out to evaluate agronomical characteristics and resistance to Fusarium wilt in tetraploid banana hybrids. The experiment was led in the experimental field at Embrapa Cassava and Tropical Fruits in a complete randomized design with 14 treatments and 10 replicates in the years 2000 and 2001. Fourteen tetraploids were evaluated: FHIA-03, PV03-44, PC42-01, PV42-53, PV42-68, PV42-81, PV42-85, PV42-129, PV42-142, PV42-143, SH3640, ST12-31, ST42-08 and YB42-21 and the Silk cultivar used as the control. The following characteristics were evaluated: plant height (m) and pseudostem diameter (cm) at 30cm from the ground, bunch weight (kg), hand weight (kg) and fruit weight (g), number of hands per bunch, fruits per hand and days to flowering until harvest and Fusarium wilt incidence. The mean values of the genotypes were grouped by the Scott Knott test at 5% significance. There is a broad variation regarding the characteristics evaluated. FHIA 03, ST12-31, SH3640, PV42-142, PV42-53 and PV42-68 present good agronomical characteristics as well as resistance to Fusarium wilt.Index terms: Musa spp., evaluation, plant breeding, Fusarium.

Sistema de pré-aviso para o controle da sigatoka-amarela da bananeira no Recôncavo Baiano

Yellow Sigatoka (Mycosphaerella musicola Leach) is one of the most serious banana diseases in Brazil, it can cause yield losses higher than 50%. The main control method has been based on spraying fungicides. The use of a monitoring system able to indicate the appropriate moment for spraying fungicide, is a very important alternative to rationalize its uses. This work aimed to defining a Total Sum value for the biological forecasting system that allows to reduce the number of annual fungicide applications needed for Yellow Sigatoka control in Reconcavo Baiano Region. The work was carried out at Embrapa Cassava & Fruits, of the Brazilian Agricultural Research Corporation - EMBRAPA , located in the Municipality of Cruz das Almas, State of Bahia. Eight treatments were evaluated: six of them using pre-established Total Sum values of the biological forecasting system (1000; 1300; 1600; 1900; 2200 and 2500), the sistematic disease control by fungicide spraying every 21 days, and the control treatment without spraying. The treatments consisted of eight plots containing 48 plants each, of the cultivar Grand Naine. Every week, ten plants of each treatment were evaluated for rate of leaf emission and disease incidence in the leaves 2, 3 and 4, in order to determine the highest degree of lesion intensity. The weekly data were used to calculate the respective Total Sum values thus indicating the necessity or not of fungicide application (propiconazole, 3 mL, plus mineral oil, 1 L). At harvest, data on production and disease severity were taken. Only three of the evaluated treatments were statistically different from the control treatment without sprayings: fungicide application every 21 days; fungicide application when the Total Sum reached 1,300; and fungicide application when the Total Sum reached 1,600. Considering the yield obtained and the number of fungicide applications required during the crop cycle, it is concluded that, for the Reconcavo Baiano Region, the application of the biological forecasting system for chemical control of Yellow Sigatoka should be performed when the Total Sum reaches 1,600. This system allowed a decrease in the number of fungicide application from thirteen to eight per year, that means 40% less fungicide used without decreasing yield.

Distribution and impact of black sigatoka in the banana plantations in the State of Acre

A sigatoka-negra (Mycosphaerella fijiensis) e a doenca de maior severidade que afeta as cultivares de banana (Musa spp.) de importância economica no mundo. Foi constatada no Brasil em 1998, no Estado do Amazonas, e tem se disseminado pelo Estado do Acre, atacando severamente as cultivares do Subgrupo Terra (AAB). Realizou-se um diagnostico da sigatoka-negra e dos impactos economicos causados por esta doenca nos municipios do Estado do Acre. Foram visitados plantios em 16 municipios e amostras de folhas de bananeiras com sintomas caracteristicos da doenca foram coletadas para diagnostico. Verificou-se que a sigatoka-negra estava presente em todos os municipios visitados. As consequencias economicas da doenca podem ser evidenciadas pela reducao de 42% na producao total de banana do Estado do Acre no periodo de 2000/2001, enquanto o valor da producao foi reduzido em 47% no ano de 2001, com repercussao nos diversos segmentos da cadeia produtiva. Nesse aspecto, observou-se que os municipios de Placido de Castro e Acrelândia, foram os mais afetados pela sigatoka-negra.