A purification procedure (Zeeet al. 1987) for closterovirus‐like particles associated with grapevine leafroll disease was improved after various sources of plant tissues, extraction buffers, pH values, and centrifugation techniques had been examined. An antiserum against the CA‐4 isolate was produced and used in ELISA. The virus‐like particles of the NY‐1 isolate measured in crude plant preparations were about 1,800 to 1,900 nm long. The molecular weight of coat protein of the NY‐1and NY‐2 isolates were ca. 43 × 103 daltons in SDS‐PAGE analysis; and bands having this molecular weight reacted in Western blotting tests with specific polyclonal and monoclonal antibodies. A large dsRNA molecule (ca. 10 × 106 Mr) along, with lower molecular weight species were isolated from leafroll diseased grapevines, but not from healthy grapevines. Seven leafroll isolates were tested for their serological relatedness in a protein A‐gold labelling immunosorbent electron microscopy, assay. Results indicated that serologically distinct serotypes existed, and mixed infection of grapevines with different scrotypes was common. A grouping of isolates into serotype I, II, III, IV is proposed.

Incidence and nematode population densities of plant-parasitic nematodes were determined in 64 samples of soil and grapevine roots collected from commercial vineyards in southern Spain between October 2003 and May 2005. In addition, a histopathological study was done of root-stock roots naturally infected by root-knot nematodes (Meloidogyne spp.). Nematodes infecting the rootstocks were identified according to conventional procedures, and the Meloidogyne spp. were furthermore identified by sequence characterized amplified region-polymerase chain reaction (SCAR-PCR) and isozyme esterase analyses. The most important plant-parasitic nematodes detected, in order of decreasing frequency of total soil infestation and root infection (percentage of samples), were Mesocriconema xenoplax (34.4%), Meloidogyne incognita (26.6%), Meloidogyne javanica (14.1%), Xiphinema index (12.5%), Xiphinema italiae (10.9%), Pratylenchus vulnus (6.3%), and Meloidogyne arenaria (1.6%). No disease symptoms were observed on aboveground plant parts of the infected grapevines, except for plants in some fields where soil was infested with the virus-vector nematodes X. index and X. italiae. Those grapevines showed a yellow mosaic pattern in leaves early in the growing season and the internode shortening characteristic of infections by Grapevine fanleaf virus. Rootstocks infected by root-knot nematodes (Meloidogyne spp.) showed distorted feeder roots and large- to moderate-sized root galls, present either singly or in clusters. Histopathology of galled roots showed a typical susceptible response to infection by root-knot nematodes: cellular alterations were induced in the cortex, endodermis, pericycle, and vascular system, including giant-cell formation and severe distortion of vascular tissues. Most Meloidogyne egg masses ocurred on the surface of the galled root tissues, a position that could facilitate dispersion of the nematode eggs and juveniles and the occurrence of secondary infections. Some of the grapevine rootstocks surveyed in this study (Paulsen 1103, Richter 110, Rupestris du Lot, and SO4) had previously been reported to be resistant to Meloidogyne spp.; however, the population densities of these nematodes found in soil and roots sampled in the present study, as well as the compatible host-parasite relationship revealed by histopathology, indicate a susceptible response to Meloidogyne spp. from southern Spain.

The temporal progress of malformation (MM) of mango (Mangifera indica) was studied from 1993 to 1995 with three management technologies applied to commercial plantations in North Guerrero, Mexico. Management influenced shoot production and thus determined the dynamics of epidemics. Environmental factors also affected disease incidence, particularly through an apparent effect on inoculum dispersal. In general, integrated management (IM), consisting of pruning, acaricide, and fungicide sprays, resulted in slower rates of epidemic development, lower levels of initial and final disease, and lesser areas under the disease progress curves. In the first cycle, IM increased yield per tree by 51% in relation to high technology (HT) and 74% in relation to lower traditional technology (LT), representing a benefit-cost rate of 2.8 and 3.3, respectively. Change of malformation incidence was correlated positively with the number of macroconidia of Fusarium sp. trapped in the canopy (r = 0.90, P = 0.0001) and wind speed (r = 0.83, P = 0.0001); both variables lagged over a 4-month period. The greatest change in malformation occurred during the main vegetative flush, which occurred 3 to 6 months after picking the fruit (May). The accumulated proportion of diseased shoots was correlated with the following variables measured over a 1-week period: average maximum daily temperature (r = -0.68, P = 0. 01), average temperature per hour (r = -0.59, P = 0.04), average number of hours with relative humidity ≥60% (r = -0.82, P = 0.001), and wind speed (r = 0.94, P = 0.0001). In general, the greatest spore density was found during the rainy season, with a morning periodicity showing the highest correlation with wind speed (r = 0.812, P = 0.0001). F. subglutinans was isolated consistently from diseased (86%) and asymptomatic (5%) vegetative and flowering shoots.

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The temporal progress and spatial distribution of papaya ringspot virus (PRV) and populations of aphid vectors were monitored in two papaya (Carica papaya) plantations in the state of Veracruz, México. The incidence of PRV had a typical sigmoidal curve and the logistic model was more acceptable for describing the disease progress than the Gompertz model. The rate (rL of increase in disease incidence (0.034 and 0.023/unit/day in Plot A and B, respectively) differed (P = 0.05) between the plots; differences in number of aphids trapped could account for the difference. The initial determination of an apparent regular spatial pattern early in the epidemic, obtained with a quadrat size determined by Greig‐Smith's method (n = 8 plants/quadrat) at 50 % disease incidence, was inconsistent with our biological observations in the field. An arbitrarily selected, square quadrat size (n = 9 plants/quadrat), was more consistent with visual observation for describing the spatial pattern in the field. With 9 plants/quadrat a random pattern was found. Aphid populations had a bimodal distribution at both sites with the highest population peak in December–February and a secondary peak in August–September and change in disease incidence was generally related to the aphid population level in the previous month. None of the five potential aphid vectors (Myzus persicae, Aphis gossypii A. nerii, A. citricola and Macrosiphon euphorbiae) of PRV in Mexico colonized the papaya plants, however, which may explain the absence of clustering of disease.