The aims of the present study were to assess the efficiency of hybrid sorghum mixtures for the management of anthracnose and analyze the virulence diversity and structure in the pathogen populations developed in response to these mixtures. Proportions of 25%, 50% and 75% of the susceptible BRS304 hybrid in relation to the resistant IG150 hybrid were evaluated. Six weekly evaluations of severity were performed. The data were transformed into area under disease progress curve (AUDPC). The isolates of Colletotrichum sublineolum were sampled from hybrid mixtures cultivated in Sete Lagoas and Indianópolis (Brazil) as well as sorghum fields in Rio Verde and Paraúna (Brazil). The increase in the proportion of the resistant hybrid in the mixtures led to a reduction in anthracnose severity. The most effective proportions were those with 25% and 50% of the susceptible variety blended with the resistant variety. Complex breeds of C. sublineolum predominated in the populations and a reduction in phenotype diversity was observed. This reduction in diversity was attributed to deviations in the degree of polymorphism in relation to virulence. However, the increase in complex breeds did not imply lesser efficiency on the part of the resistant hybrid in conferring protection to the susceptible hybrid.

A preservação de urediniósporos de Puccinia psidii na ausência do hospedeiro é necessária para vários estudos biológicos, tais como patogenicidade e técnicas moleculares. Neste trabalho, foi avaliada a viabilidade e a infectividade desses urediniósporos em nitrogênio líquido (-196ºC), deep-freezer (-80ºC), geladeira (5ºC), BOD (25ºC) e material herborizado (25ºC). Os urediniósporos foram multiplicados em plantas de jambeiro (Syzygium jambos) e armazenados nos ambientes citados por seis meses e, a cada 30 dias, avaliados quanto à germinação in vitro e a infectividade em plantas de Eucalyptus grandis. Não houve preservação da viabilidade e da infectividade de urediniósporos armazenados em BOD e em material herborizado (25ºC). A germinação de urediniósporos (24,9%) e a infectividade (162 pústulas/folha) em ambiente de geladeira-modificado foram maiores aos 17,6 e aos 30 dias, respectivamente. A maior eficiência na manutenção de germinação dos urediniósporos armazenados em "deep-freezer" (34,3) e nitrogênio líquido (36,3) ocorreu aos 45 e 40 dias respectivamente. Enquanto que, a maior infectividade desses urediniósporos foi de 77 pústulas/folha aos 60 dias para "deep-freezer" e 67 pústulas/folha aos 90 dias para nitrogênio líquido. Os urediniósporos mantidos no "deep-freezer", no nitrogênio líquido e em geladeira-modificado permaneceram viáveis e infectivos até 150 dias.

The objective of this study was to evaluate the viability and infectivity of urediniospores stored in liquid nitrogen (-196ºC), deep-freezer (-80ºC), modified-refrigerator (5ºC), biochemical oxygen demand (BOD 25ºC) and herbarium specimens (25ºC), for 150 days. The urediniospores were multiplied in Rose Apple plants (Syzygium jambos) and stored in the above conditions. Every 30 days, the germination and infectivity were evaluated, the first in vitro and the second on Eucalyptus grandis plants. The viability and infectivity of urediniospores stored in BOD and herbarium specimens were not preserved. The maximum germination (24.9%) and infectivity (162 pustules/leaf) occurring in modified-refrigerator environment were higher at 17.6 and 30 days, respectively. Urediniospore germination was highest when preserved in deep-freezer (34.3%) and liquid nitrogen (36.3%), at 45 and 40 days, respectively. The highest infectivity occurred at 60 days for the deep-freezer (77 pustules/leaf) and 90 days for the liquid nitrogen (67 pustules/leaf). Urediniospores kept in deep-freezer, liquid nitrogen, and modified-refrigerator maintained their viability and infectivity for 150 days.