Symptoms Of Different Severity Research Articles

Sweetpotato Virus Disease (SPVD): Distribution, Incidence, and Effect on Sweetpotato Yield in Peru.

Sweetpotato virus disease (SPVD), the most important disease affecting sweetpotato (Ipomoea batatas (L.) Lam), is caused by the synergistic interaction of the aphid-transmitted Sweetpotato feathery mottle virus (SPFMV) and whitefly-transmitted Sweetpotato chlorotic stunt virus (SPCSV). In this study, SPVD was the main disease in the Cañete Valley, the major sweetpotato-producing area in Peru. Studies on virus incidence showed that SPCSV and SPFMV were the most frequently identified viruses in Cañete Valley. Symptoms of different severity were associated with isolates of both viruses involved in the SPVD. Over 80% of plants infected with both SPFMV and SPCSV showed the symptoms (leaf reduction and deformation, vein clearing or mosaic, and stunting) typically attributed to SPVD elsewhere. SPFMV did not significantly affect the yield of the sweetpotato cultivars Jonathan and Costanero, but infection of these cultivars by SPCSV was associated with significant yield reduction. Double infection by the two viruses resulted in SPVD and greater yield reduction than for either alone. These results demonstrate that SPFMV and SPCSV interact synergistically and that the severity of SPVD symptoms also depends on the particular isolate of each virus.

Role of a novel type of double infection in the geminivirus‐induced epidemic of severe cassava mosaic in Uganda

SummaryTo study the cause of the current epidemic of severe mosaic in Ugandan cassava, PCR analysis was used to detect and identify African cassava mosaic virus (ACMV), East African cassava mosaic virus (EACMV) and the recently reported recombinant geminivirus (UgV), which is derived from ACMV and EACMV, in leaf extracts from cassava plants grown from cuttings in the glasshouse at Dundee. The cuttings were collected from plants showing symptoms of different severities and growing at different sites in Uganda inside, at the periphery of, and outside, the area affected by the epidemic. ACMV occurred throughout the nine districts sampled but UgV was detected only in the area affected by the epidemic. EACMV was not found in Uganda. Most plants containing ACMV alone expressed mild or moderate mosaic, whereas very severe mosaic developed in most plants containing UgV plus ACMV and a few of those containing UgV only. Very severe mosaic in cassava from southern Sudan was likewise associated with co‐infection by UgV and ACMV. The very severe disease was reproduced by graft‐inoculating geminivirus‐free cassava with UgV plus ACMV; plants inoculated with either UgV or ACMV developed severe or moderate symptoms, respectively. Unlike ACMV, Malawian EACMV did not enhance the severity of symptoms induced by UgV. However, a very severely affected plant from Ukerewe Island, Tanzania, contained ACMV and EACMV but not UgV. UgV attained a much greater concentration in cassava than did ACMV but the opposite occurred in Nicotiana benthamiana. In neither host was total virus antigen concentration affected by co‐infection.Factors affecting the genesis, selection and spread of UgV are discussed. The evidence indicates that UgV is probably of relatively recent origin, that such variants do not appear often, and that the current epidemic has resulted from the rapid spread of UgV to infect plants and to invade regions in which ACMV already occurred. The novel type of virus complex so produced, consisting of an interspecific recombinant virus (UgV) and one of its parents (ACMV), typically has even more severe effects than UgV alone.

Nonspecific Phytotoxic Effects of Sirodesmins on Host and Nonhost Plants of Leptosphaeria maculans

AbstractSirodesmin PL, deacetylsirodesmin PL and sirodesmin C were isolated from cultures of an aggressive strain of Leptosphaeria maculans, purified by thin layer and column chromatography, and tested on leaves and roots of 14 host and non‐host plants of the pathogen. The sirodesmins showed no host‐specificity. However, various plant species developed symptoms of different severities. In both bioassay systems deacetylsirodesmin PL had a lower phytotoxicity than sirodesmin PL and sirodes‐min C. Our results show that sirodesmins belong to the non‐host‐specific phytotoxins.

Purification, chemical characterization and host-specificity of the toxin produced by Alternaria brassicae

A chromatographic procedure was developed to purify the toxin produced in culture by Alternaria brassicae. The procedure included gel filtration, adsorption on charcoal, silicic acid chromatography and high pressure liquid chromatography. Fast atomic bombardment spectrum of the purified toxin showed protonated molecular ion peak at relative intensity 594. High resolution mass spectrometry gave an exact mass of 593·3791 with a molecular formula C 30H 51N 5O 7 (calculated molecular weight = 593·3788). Negative ninhydrin reaction of the toxin and the presence of amino acids in the toxin hydrolysate indicated that the toxin is a cyclic peptide. Molecular weight, ninhydrin reaction, amino acid composition, proton nuclear magnetic resonance spectrum, HPLC retention time, and symptomatology and activity of the toxin on hosts and non-hosts of A. brassicae were identical to those of Destruxin B. Both the fungus and the toxin caused symptoms of different severities on different brassicas, ranging from severe chlorosis and necrosis to almost no visible chlorosis. The order of sensitivity of different brassicas to the toxin was similar to their order of susceptibility to A. brassicae. The toxin was also able to distinguish susceptibility differences within the species Brassica campestris. It did not cause symptoms on nine plant genera which are non-hosts of A. brassicae. The degrees of toxin sensitivity of all plants tested were correlated with their degrees of susceptibility to A. brassicae, suggesting that the activity of the toxin is host-specific. This is the first report on the host-specific nature of a toxin produced by A. brassicae.