Co-infection of two criniviruses and a begomovirus enhances the disease severity in cucumber

European Journal of Plant Pathology - In the past two decades, viruses in the genera Crinivirus and Begomovirus, transmitted by whiteflies, have emerged as threatening diseases to cucurbit...     

Antimycotic activities of selected plant flora,growing wild in Lebanon,against phytopathogenic fungi

Petroleum ether (PE) and methanolic extracts of nine wild plant species were tested in vitro for their antimycotic activity against eight phytopathogenic fungi. The efficacy of PE extracts against all pathogens tested was higher than that of methanolic extracts. Wild marjoram (Origanum syriacum) PE extract showed the highest and widest range of activity. It resulted in complete inhibition of mycelial growth of six of eight fungi tested and also gave nearly complete inhibition of spore germination of the six fungi included in the assay, namely, Botrytis cinerea, Alternaria solani, Penicillium sp., Cladosporium sp., Fusarium oxysporum f. sp. melonis, and Verticillium dahlia. The other plant extracts showed differential activities in the spore germination test, but none was highly active against mycelial growth. Inula viscosa and Mentha longifolia were highly effective (>88%) in spore germination tests against five of six fungi tested, whereas Centaurea pallescens, Cichorium intybus, Eryngium creticum, Salvia fruticosa, and Melia azedarach showed >95% inhibition of spore germination in at least two fungi. Foeniculum vulgare showed the least antimycotic activity. Fractionation followed by autobiography on TLC plates using Cladosporium sp. as a test organism showed that O. syriacum PE extracts contained three inhibition zones, and those of Inula viscosa and Cichorium intybus, two, whereas the PE extracts of the remaining plants showed each one inhibition zone. Some of the major compounds present in these inhibition zones were identified by GC-MS. The possibility for using these extracts, or their mixtures, to control plant diseases is discussed.     

Comparison of the reaction of tomato lines to infection by tomato yellow leaf curl begomovirus in Lebanon

Tomato yellow leaf curl begomovirus (TYLCV), transmitted by the whitefly Bemisia tabaci , is epidemic in Africa, the Middle East and South-East Asia. It is also reported in some European countries and the American continent. In Lebanon, it is the major limiting factor for summer and autumn production of tomato. Comparison of the nucleotide sequence in the intergenic region with other reported leaf curl viruses showed the Lebanese TYLCV isolate to be closely related to Egyptian, Israeli and Jamaican isolates (94–96% identity). However, it is not closely related to isolates from Sardinia, Spain and Thailand, or to tomato leaf curl isolates from India, Taiwan and Australia. In field and greenhouse screening tests conducted for 5 years on 67 tomato lines, several were identified as promising. TY-Carla, PSR and RS lines were among the most promising with determinate growth, while S&G 143 and the DR lines were the most promising with semi-determinate and indeterminate growth, respectively. Virus concentrations in most, but not all, tolerant tomato lines were significantly lower than in the susceptible lines. None of the lines tested was immune to the virus. A survey of TYLCV alternative hosts on at least 58 plant species, using nucleic acid hybridization, showed that Amaranthus sp., Malva sp., Sonchus oleraceus , Plantago sp., Solanum melongena , Phaseolus vulgaris and Mercurialis annua may play an important role in the epidemiology of TYLCV in Lebanon. Mercurialis annua is a newly reported host for TYLCV.