Infectivity analysis of a soybean isolate of Mungbean yellow mosaic India virus by agroinoculation

Yellow mosaic disease (YMD) of legumes endemic to South Asia are caused by begomoviruses transmitted by whiteflies. Based on molecular characterization, two distinct viruses – Mungbean yellow mosaic India virus (MYMIV) and Mungbean yellow mosaic virus (MYMV) – were found previously to be the etiological agents of YMD in legumes. Here, host range studies with a soybean isolate of MYMIV (MYMIV-[Sb]) were carried out by both whitefly transmission and agroinoculation. MYMIV-[Sb] was similar to a cowpea isolate of MYMIV (MYMIV-[Cp]) in its ability to infect cowpea, thus differing from blackgram (MYMIV) and mungbean (MYMIV-[Mg]) isolates, which do not infect cowpea. Genomic analysis of DNA A and DNA B components of these MYMIV isolates show characteristic differences in complete DNA B nucleotide sequence correlating with host range differences.     

First isolation of rose yellow mosaic virus in Japan

Rose yellow mosaic virus, which belongs to the Roymovirus genus in the Potyviridae family, was isolated here in Japan from a rose cultivar, Irish Mist. The full-length genomic sequence was similar to a strain in Minnesota, United States, which was the first ever isolated, with 85% nucleotide and 94% amino acid sequence similarities. Unlike the Minnesota strain, which lacks 220 nt including the 6K1 protein region, the Japanese isolate contains this coding region, which is commonly found in those of the Potyviridae.

     

First report of cucumber mosaic cucumovirus in banana from Pakistan

During regular surveys of banana plantations in the Sindh province of Pakistan for banana bunchy top nanavirus (BBTV), sporadic plants showing mosaic, chlorotic spots intermingled with a dark green area were observed at a few places in the districts of Thatta, Hyderabad and Nawabshah. The infected young plants were uprooted and grown in pots for 2 years to ascertain the cause of the disease. Apart from studying the development of symptoms, the infected plants were tested for the presence of BBTV, cucumber mosaic cucumovirus (CMV), chilli veinal mottle potyvirus (CVMV), tomato mosaic tobamovirus (TMV), potato X potexvirus (PVX) and potato Y potyvirus (PVY) by DAS-ELISA. Virions were also partially purified. The infected plants developed typical symptoms of CMV. All tested plants were ELISA-positive only for CMV, and a partially purified preparation revealed virus particles measuring 25–28 nm in diameter. Based on the characteristic field symptoms, serology and particle morphology, the presence of CMV in banana in Pakistan was established.     

Zucchini yellow mosaic virus

Zucchini yellow mosaic potyvirus (ZYMV), first isolated in Italy in 1973, described in 1981, and then identified in all continents within a decade, is one of the most economically important viruses of cucurbit crops. It is efficiently aphid-transmitted in a nonpersistent manner and it is also seed-borne in zucchini squash, which could have contributed to its rapid spread worldwide. Biological variability has been observed among ZYMV isolates, concerning host range, symptomatology and aphid transmissibility. More recent studies also revealed a serological and molecular variability. The survival of ZYMV in areas where cucurbits are not grown throughout the year remains to be elucidated, because very few natural over-wintering hosts have been identified so far. Partial control of ZYMV can be achieved by limiting transmission of the virus to the crops by aphids, using adapted cultural practices. Cross-protection with a mild strain has been shown to be effective against most ZYMV isolates. Resistance genes found in cucurbit germplasms are currently being introduced into cultivars with good agronomical characteristics. Pathogen-derived resistance strategies using the expression of ZYMV genes in transgenic plants have also been developed and appear promising. Nevertheless, the high biological variability of ZYMV justifies a careful evaluation of the deployment of genetic control strategies in order to increase their durability.