Xanthomonas axonopodis pv. citri strains that cause disease in citrus were investigated by pulsed field and plasmid profile analysis. For the first method, genomic DNA was digested by the rare-cutting enzymes Xba I and Vsp I. The strains evaluated were collected in seven different States of Brazil and in Argentina, Bolivia, Paraguay and Uruguay. Genetic variability was found among strains of X. axonopodis pv. citri from different geographical areas Argentina, Bolivia and Uruguay, with similarities varying from 0.62 to 0.83. However, the strains collected in Brazil, despite being from different States, have shown a genetic similarity ranging from 0.83 to 1.00. Cluster analysis showed a relationship between genomic similarity and geographical origin of the strains. Plasmids were observed in all strains, with a total of five different plasmids, with sizes between 57.7 and 83.0 kilobases. The 72.6 kb plasmid was the most frequent, present in 15 out of 22 strains, while the 68.1 kb plasmid was observed in two strains only. Although the plasmid diversity detected in the present study was not very great, the X. axonopodis pv. citri strains evaluated showed a considerable degree of diversity with regard to this extrachromosomal genetic element.

Mudas de cafeeiros da cultivar Mundo Novo de Coffea arabica foram mantidas sem irrigação em viveiro, por um período de 32 dias consecutivos, com o objetivo de se avaliar o efeito do potencial de água na folha nos danos causados por baixas temperaturas, sob condições controladas. As plantas avaliadas apresentaram potenciais de água nas folhas entre -0,45MPa (solo encharcado) no início do período experimental e -4,8MPa (murchamento severo das folhas) na fase final. Os tratamentos com baixas temperaturas consistiram em submeter as plantas de café protegidas com sacolas plásticas seladas durante 90 minutos a -3ºC ± 0,5ºC, dentro de um banho de solução etanólica. A avaliação dos danos foliares foi feita visualmente por quatro avaliadores independentes, um dia após a submissão às baixas temperaturas. Os resultados mostraram que, sob estresse hídrico moderado, houve maior frequência de plantas não danificadas e menor freqüência de plantas com danos severos. Plantas muito hidratadas sofreram danos severos com maior frequência. Estes resultados podem explicar parte da variabilidade regional nos danos de geadas e destacam a importância de novos estudos associando tolerância ao frio com tolerância à seca.

Young coffee plants from cultivar Mundo Novo of Coffea arabica were grown without irrigation for 32 consecutive days, to evaluate the effect of leaf water potential on damage caused by low temperatures, under controlled conditions. A wide range of leaf water potentials were evaluated, from - 0.45MPa (wet soil) at the beginning of the experimental period, to - 4.8MPa (severe leaf wilting) at the end. Results showed that under moderate water stress, there was a higher frequency of undamaged plants and lower frequency of severely damaged plants. These results help explain part of the regional variability observed after a frost and stress the importance of new studies associating cold and drought tolerance in coffee.