Severe Verticillium dahliae attacks have occurred in artichoke crops in the Comunidad Valenciana region of eastern-central Spain since the late 1990s. Knowledge of genetic and virulence diversity in the pathogen population is a key factor for the management of the disease through disease risk assessment as well as development and use of resistant cultivars. V. dahliae isolates from artichoke (109 isolates) and cotton (three isolates) in that region were characterized by vegetative compatibility grouping (VCG), and specific polymerase chain reaction assays using three sets of primer pairs that differentiate the cotton-defoliating (D) and -nondefoliating (ND) V. dahliae pathotypes. In all, 35 and 39 V. dahliae isolates representative of the identified VCGs and geographic origins were tested for virulence to artichoke cvs. Nun 6374 and Nun 9444, and cotton cv. Acala SJ-2, respectively. Four VCGs were identified among 107 artichoke isolates, and 2 isolates were heterokaryon self-incompatible: VCG1A (one isolate), VCG2A (31 isolates), VCG2B (72 isolates), and VCG4B (three isolates). The three cotton isolates were VCG1A. Isolates in VCG2B were distributed across the region and were the most prevalent isolates in the northern part. Conversely, 83.9% of isolates in VCG2A were recovered from the southern part of the region. Two subgroups of isolates were identified in VCG2B based on heterokaryon compatibility with either international or local tester isolates, which further showed diversity in the amplification of 334- and 824-bp DNA fragments which are markers of the D and ND pathotypes, respectively. Virulence of isolates to artichoke and cotton correlated with VCG but the pattern of correlation varied with the host. VCG1A isolates from artichoke and cotton induced defoliation in cotton but not in artichoke. Collectively, isolates of VCG2B and VCG4B were the most virulent and isolates of VCG1A or HSI were the least virulent to artichoke; but isolates of VCG1A were more virulent to cotton than those of any other VCG. Also, molecular subgrouping in VCG2B determined by amplification of the 334- and 824-bp markers correlated with virulence of isolates to the two hosts tested.

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Verticillium dahliae isolates recovered from a new focus of severe Verticillium wilt of cotton in the northeast of Israel were tested for vegetative compatibility using nitrate non-utilizing (nit) mutants and identified as VCG1, which is a new record in Israel. Other cotton isolates of V. dahliae from the northern and southern parts of the country were assigned to VCG2B and VCG4B, respectively. VCG1 isolates induced severe leaf symptoms, stunting and defoliation of cotton cv. Acala SJ-2, and thus were characterized as the cotton-defoliating (D) pathotype, whereas isolates of VCG2B and VCG4B were confirmed as the earlier described defoliatinglike (DL) and non-defoliating (ND) pathotypes, respectively. This is the first record of the Dpathotype in Israel. The host range of representative isolates of each VCG-associated pathotype was investigated using a number of cultivated plants. Overall, the D isolates were more virulent than DL isolates on all tested host plants, but the order of hosts (from highly susceptible to resistant) was the same: okra (Hibiscus esculentus local cultivar), cotton (Gossypium hirsutum cv. Acala SJ2), watermelon (Citrullus lanatus cv. Crimson Sweet), safflower (Carthamus tinctorius cv. PI 251264), sunflower (Helianthus annuum cv. 2053), eggplant (Solanum melongena cv. Black Beauty), and tomato (Lycopersicon esculentum cv. Rehovot 13). The pattern of virulence of ND isolates differed from that of D and DL isolates, so that the former were highly virulent on eggplant but mildly virulent on cotton. Tomato was resistant to all cotton V. dahliae isolates tested. RAPD and specific PCR assays confirmed that the D isolates from Israel were similar to those originating from other countries.

and increase in fue incidence of plants showing follar symptoms and fue Jiménez-Díaz, R. M. 1995. lnfluence of inoculum density of defoliating disease intensity index over the accumulated physiological time from and nondefoliating pathotypes of Verticillium dahliae on epidemics of sowing. For similar levels of initial inoculum, fue defoliating pathotype Verticillium wilt of cotton in southem Spain. Phytopathology 85:1474-of ~ dahliae caused an earlier epidemic onset, a higher cate of increase 1481. in fue incidence of follar symptoms and fue disease intensity index over physiological time, and a higher final amount of both disease measure-Linear regression analysis of data transformed according to several ments than the nondefoliating pathotype. Also, for fue two disease mathematical models showed no significant correlation between the measurements, fue rate of progress increased with fue initial inoculum inoculum density of Verticillium dahliae deterrnined at sowing time in density of fue defoliating pathotype up to a threshold of 24 to 44 CFU/g randomly chosen cotton fields and fue incidence of plants with vascular of dry soil in 1986 and 44 to 75 CFU/g of dry soil in 1987. Differences discoloration, fue incidence of plants with follar symptoms, or a disease in severity among Verticillium wilt epidemics were described more apintensity index for Verticillium wilt of cotton calculated at fue end of fue propriately by fue descriptive parameters of fue increase in the disease crop season. Epidemic development of Verticillium wilt in cotton was intensity index over physiological time than by fue corresponding painvestigated in field plots naturally infested with different inoculum rameters of fue increase in fue incidence of follar symptoms. densities of fue defoliating and nondefoliating pathotypes of ~ dahliae in 1986 and 1987. The straight line model adequately described fue

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