A Survey of Infectious Diseases and Parasites of Penaeid Shrimp from the Gulf of Mexico

A histopathological survey of wild and cultured shrimp from the Gulf of Mexico was carried out to determine the prevalence and severity of infectious diseases and parasites, affecting four species of penaeid shrimp (Litopenaeus setiferus, Farfantepenaeus aztecus, F. duorarum, and L. vannamei). Around 60 shrimp were obtained from each of 10 sampling stations during different months in 1999 and 2000. One station was a shrimp culture farm from Tamaulipas State, and nine were wild stations from Tamaulipas (five), Veracruz (one), and Campeche (three) States. Thirty shrimp from each station were used for histological analysis. The remaining shrimp were frozen and kept at ?20 C to carry out PCR techniques to determine the presence of white spot syndrome virus (WSSV). Some in situ hybridization analyses were applied to ascertain cases of WSS viral disease. Fresh analysis was carried out in shrimp from only one station for parasite identification. The histopathological survey performed on 688 shrimp showed no evidence of viral diseases. Two shrimp from one station were histologically diagnosed as having presumptive WSSV. Tissues from the same shrimp were processed for in situ hybridization and another 20 samples from the same station were processed to run PCR techniques. In each case, the results were negative. The same PCR procedure was applied to the rest of the frozen samples and none of them showed the presence of the WSSV. No important bacterial infections were observed in any of the wild or cultured shrimp analyzed. Fresh analysis demonstrated the presence of the cestode Prochristianella hispida and the gregarines Cephalolobus penaeus and Nematopsis penaeus. Histological analysis showed that the abundance of P. hispida varied from 7 to 90%, and G1 to G4 grades of severity were observed, with G1 being the most common. Gregarines were commonly observed in the histological slides, with a prevalence varying from 3 to 56% and G1 severity in most cases. Haplosporidan infection was observed in one sample of F. duorarum, which is the first report of this parasite in this host. Two invasive epibionts, the filamentous bacteria Leucothrix sp. and the ciliate Ascophrys sp., were found in four sampled stations. The study showed that in ten stations sampled from 1999 to 2000 in the Gulf of Mexico, shrimp populations had no serious infectious diseases.     

Traits related to drought resistance in common bean

Common bean (Phaseolus vulgaris L.) is grown in regions where water deficits during reproductive development significantly reduce yield. The purpose of this study was to evaluate the association of specific phenological and physiological traits with drought resistance in common bean. Five genotypes were grown under and near a rain shelter in 1988, and an additional 16 progeny lines were included in 1990. Drought stress determined by the drought intensity index was severe (0.78) in 1988 and more moderate (0.63) in 1990. Water stress reduced the expression of most traits with the exception of days to flower and leaf moisture retention capacity. Seed yield among genotypes was reduced from 22 to 71% due to drought. Yield under stress was correlated with yield under nonstress in 1990 and negatively correlated with the drought susceptibility index in 1988. Yield components which exhibited the largest differential genotypic responses to stress were pod and seed number, whereas seed size was more stable. Genotypic variation was detected in all the partitioning indexes, chiefly harvest index and relative sink strength, and the heritability estimates for these traits were high. The limited genetic variability observed among water relations traits and their role in water conservation would restrict their potential use in the selection for drought resistance in common bean. The differential correlations between phenological, biomass and partitioning traits and the indexes for yield and drought susceptibility would suggest that the most effective approach in breeding for drought resistance in common bean would be based first on selection for high geometric yield followed by selection among the high-yielding individuals for low to moderate levels of the drought susceptibility index. This revised version was published online in July 2006 with corrections to the Cover Date.     

Foliar response of wild and domesticated Phaseolus vulgaris L. to water stress

It is surmised that domestication has reduced geneticvariability in the common bean (Phaseolusvulgaris L.). However, little is known about leaf anatomy responses to water stress in wild or domesticated forms ofP. vulgaris. In this study,anatomical variation was evaluated in watered and water stressed plants of wild and domesticated genotypes of P.vulgaris from Mexico, growing under greenhouse conditions. Five terminal leaflets of completely expanded leaves wereused to evaluate leaf area (LA) and theirmiddle-regions to evaluate leaf thickness (LT), and various anatomical features. Domesticated genotypes showed bigger LAthan that of the wild ones; there was an effect due to the origin of materials, LA being bigger in genotypes from warm and humid lands that those from dry and temperate ones. No differences were detected in LT among materials; however, in domesticated plants the palisadeparenchyma predominated over the spongy one, contrasting with thewild genotypes. Under drought conditions, stomatal abortion was observed in wild and domesticated genotypes, especially on theabaxial surface. We conclude that, in fact, there are contrasting differences in leaf anatomy among wild and domesticated forms of Mexican Phaseolus vulgaris. Results suggest that domestication not only favours the enlargement of the LA, but also an increase in palisade parenchyma, suggesting a divergence toward assimilation in domesticated forms, in contrast with a better internal gas diffusion in wild forms. Domestication seems to have accentuated stomatal abortion as means of a transpirational control mechanism to counteract the effects of drought.