Scab on pear is caused by two pathogens, Venturia pyrina on European pear and V. nashicola on Asian pear. Five races of V. pyrina and seven races of V. nashicola have been reported thus far and pathological specialization occurs in both species. Among them, the five race isolates of V. pyrina were previously found from wild Syrian pear. In this study, mating and morphological characteristics of Venturia isolates from Syrian pear were compared with those of isolates from European and Japanese pear cultivated in Japan. The results from mating experiments showed that Syrian pear isolates were compatible with European pear isolates of V. pyrina to produce ascospores but were sterile with V. nashicola isolates in culture. Interestingly, however, the size and shape of conidia collected from naturally infected leaves of Syrian pear resembled those of V. nashicola. This finding may open the way to study coevolution between pear hosts and Venturia spp. in the future.

ilamentous fungi of the genus Colletotrichum and its teleomorph Glomerella are considered major plant pathogens worldwide. They cause significant economic damage to crops in tropical, subtropical, and temperate regions. Cereals, legumes, ornamentals, vegetables, and fruit trees may be seriously affected by the pathogen (3). Although many cultivated fruit crops are infected by Colletotrichum species, the most significant economic losses are incurred when the fruiting stage is attacked. Colletotrichum species cause typical disease symptoms known as anthracnose, characterized by sunken necrotic tissue where orange conidial masses are produced. Anthracnose diseases appear in both developing and mature plant tissues (4). Two distinct types of diseases occur: those affecting developing fruit in the field (preharvest) and those damaging mature fruit during storage (postharvest). The ability to cause latent or quiescent infections has grouped Colletotrichum among the most important postharvest pathogens. Species of the pathogen appear predominantly on aboveground plant tissues; however, belowground organs, such as roots and tubers, may also be affected. In this article, we deal in particular with methods used to identify and characterize Colletotrichum species and genotypes from almond, avocado, and strawberry, as examples, using traditional and molecular tools. The three pathosystems chosen represent different disease patterns of fruitassociated Colletotrichum. Multiple Species on a Single Host Numerous cases have been reported in which several Colletotrichum species or biotypes are associated with a single host. For example, avocado and mango anthracnose, caused by both C. acutatum and C. gloeosporioides, affect fruit predominantly as postharvest diseases (25,40,41). Strawberry may be infected by three Colletotrichum species, C. fragariae, C. acutatum, and C. gloeosporioides, causing anthracnose of fruit and other plant parts (31). Almond and other deciduous fruits may be infected by C. acutatum or C. gloeosporioides (Table 1) (1,5,46,50). Citrus can be affected by four different Colletotrichum diseases (61): postbloom fruit drop and key lime anthracnose, both caused by C. acutatum, and shoot dieback and leaf spot, and postharvest fruit decay, both caused by C. gloeosporioides. Additional examples of hosts affected by multiple Colletotrichum species include coffee, cucurbits, pepper, and tomato. Single Species on Multiple Hosts It is common to find that a single botanical species of Colletotrichum infects multiple hosts. For example, C. gloeosporioides (Penz.) Penz. & Sacc. in Penz. (teleomorph: Glomerella cingulata (Stoneman) Spauld. & H. Schrenk), which is considered a cumulative species and forms the sexual stage in some instances, is found on a wide variety of fruits, including almond, avocado, apple, and strawberry (Table 2) (6,15,31,46). Likewise, C. acutatum J.H. Simmonds has been reported to infect a large number of fruit crops, including avocado, strawberry, almond, apple, and peach (1,5,16,25,27). Examples of other species with multiple host ranges include C. coccodes, C. capsici, and C. dematium (14,56).

Anthracnose, caused byColletotrichum gloeosporioides, is the major disease of almond in Israel. Pathogen attack of young fruit results in fruit rot and leaf wilting. Seventy isolates ofC. gloeosporioides were obtained from affected almond fruits collected at 11 sites during 1991–2 and 1994. Chlorate-resistant nitrate-nonutilizing (nit) mutants were generated from each isolate and used in complementation (heterokaryon) tests. The formation of complementary stable heterokaryons between mutants from different isolates showed that all the isolates belonged to a single vegetative compatibility group. Representative isolates ofC. gloeosporioides from almond did not form heterokaryons with local isolates ofColletotrichum from anemone and avocado, indicating that the almond isolates constitute a distinct subspecific group withinC. gloeosporioides.

The plant disease Apple Scab, caused by the ascomycete fungus Venturia inaequalis (Cke.) Wint. (anamorph Spilocea pomi Fr.), is the single most important disease of cultivated apple (Malus domestica Borkh.) worldwide. Severe apple crop losses can result when appropriate control measures are not taken, especially when the spring and early summer seasons are moist and cool. The fungal pathogen has a pronounced low temperature requirement for the initiation of the sexual or pseudothecial stage. In temperate apple growing regions of the world, this temperature requirement is met only after leaf fall, on the orchard floor, where, in winter months, low temperatures trigger the development of pseudothecia. In the spring, overwintered pseudothecia time their production of ascospores to precisely coincide with the emergence of new leaves, thus initiating a new cycle of disease. In Israel, apple production can be divided into two ecological zones, characterized primarily by the presence or absence of low winter temperatures due to elevation: the Golan Heights (600 - 1300 m above sea level) and the Hula Valley (100 m above sea level) & the coastal plain. Only on the Golan Heights are sustained low winter temperatures present, whereas such temperatures are rare in the Hula Valley and non-existent along the coastal plain. Our hypothesis was that this intrinsic difference in Israeli apple ecology has had a direct impact on the life cycle of the pathogen, attenuating the importance of the sexual stage in low elevation apple production areas. Since sexual reproduction in this fungus has an obligate cold requirement for sustained low winter temperatures, and since these requirements in Israel are met only on the Golan Heights, we were interested in whether lower elevation populations might be comprised of asexual clonal lineages. This would have bearing on control strategies for the disease in Israel and may impact on the propensity of this pathogen to develop fungicide resistance. The present study1 was initiated to determine whether differences in genotypic diversity among populations of V. inaequalis, as detected using neutral genetic markers associated with microsatellites, were related to the ecological conditions in which apples are grown in Israel. Microsatellites are short (5 - 30bp) repeated sequences found throughout the eukaryotic genome. Since they are non-coding and under little constraint to maintain sequence conservancy, they evolve quite rapidly and provide useful genetic markers to monitor individuals in populations. In this study, genotypic diversity was measured using PCR & oligonucleotide primers designed to fungal microsatellites under high annealing temperatures (microsatellite primed or MP-PCR). Two orchards were sampled from the Golan Heights (El Rom & Ortal; n