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ABSTRACT Initial infection processes and the subsequent colonization of leaves and young stems of peach by Tranzschelia discolor were studied. On leaves where multiple disease cycles of peach rust occur during the growing season, urediniospores germinated after 4 h of wetness. Germ tubes became septate and formed appressoria only over leaf stomata beginning 18 h after inoculation. No appressoria, however, formed over stomata of positive replicas of leaf surfaces indicating nonthigmotropic responses of germ tubes. On young, primary-growth stems (ca. 8 weeks old), stomata were mostly closed, less frequent than on leaves, and recessed from the surface of the cuticle of the epidermis. Although appressoria formation was not observed on inoculated stems, germ tube growth of urediniospores was directional toward stomata. Penetration of stem tissue is apparently a less common event that was reflected by a lower occurrence of stem lesions compared with that of leaf lesions in our potted plant inoculation studies and previous field observations. Still, stem lesions are important as sources of primary inoculum each spring and were reproduced in this study for the first time. Fungal colonization of leaves and stems was subepidermal-intercellular and haustoria were commonly found within mesophyll or cortical cells, respectively. No fungal colonization was observed in cambial stem tissue. Vascular tissue was also not colonized and delimited lesions in leaves and stems. Morphological host responses were not observed in infections on either leaves or young stems. In older stems (>32 weeks old), however, the infection was delimited by a wound periderm after uredinial formation. Furthermore, with continued secondary growth, stems recovered and fungal lesions became part of the bark tissue of woody branches. Thus, the fungus must infect primary-growth branches each year to establish stem lesions. 相似文献
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ABSTRACT The development of rust epidemics caused by Tranzschelia discolor on leaves and stems of cling peach was studied in California orchards. Sporulating stems lesions were only detected from late March until July in 1997 and 1998. When rust was present in the fall, the quadratic equation Y = -82.51 + 1.97JD - 0.01JD(2) using Julian day (JD) described the incidence of sporulating lesions on stems of cv. Andross (R(2) = 0.73; P = 0.001) in the following spring season. Late-season rust epidemics occurred in 1996 and 1997. Incidence of rust on leaves of cvs. Andross and Ross was <10% from April through July and 80 to 100% by October/November. In 1998, early-season epidemics developed with disease incidence at 28 to 56% by July/August in two cv. Andross orchards. No disease was observed during the 1999 growing season. Using linear regression analysis, logistic and exponential models best described the development of disease in 1996 and 1997, respectively. In contrast, the monomolecular model best described the disease in 1998. In an analysis of variance comparing disease progress curves on cv. Andross from 1996 to 1998, no significant differences in area under the disease progress curve and rho were observed, whereas y(max) was significantly different (P < 0.001). A repeated measures analysis indicated that in a cv. Andross orchard the year of the disease progress curve, time of sampling, and their interaction were highly significant (P < 0.01). This indicated a distinct difference between early- and late-season epidemics. Earlyseason development of rust on leaves occurred in years with >/=117.3 mm of total precipitation and maximum temperatures of =30.2 degrees C in April to June. 相似文献
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ABSTRACT The early infection and colonization processes of Colletotrichum acutatum on leaves and petals of two almond cultivars with different susceptibility to anthracnose (i.e., cvs. Carmel and Nonpareil) were examined using digital image analysis of light micrographs and histological techniques. Inoculated tissue surfaces were evaluated at selected times after inoculation and incubation at 20 degrees C. Depth maps and line profiles of the digital image analysis allowed rapid depth quantification of fungal colonization in numerous tissue samples. The results showed that the early development of C. acutatum on petals was different from that on leaf tissue. On petals, conidia germinated more rapidly, germ tubes were longer, and fewer appressoria developed than on leaves. On both tissues, penetration by the pathogen occurred from appressoria and host colonization was first subcuticular and then intracellular. On petals, colonizing hyphae were first observed 24 h after inoculation and incubation at 20 degrees C, whereas on leaves they were seen 48 to 72 h after inoculation. Intercellular hyphae were formed before host cells became necrotic and macroscopic lesions developed on petals >/=48 h and on leaves >/=96 h after inoculation. Histological studies complemented data obtained by digital image analysis and showed that the fungus produced infection vesicles and broad hyphae below the cuticle and in epidermal cells. In both tissues, during the first 24 to 48 h after penetration fungal colonization was biotrophic based on the presence of healthy host cells adjacent to fungal hyphae. Later, during intercellular growth, the host-pathogen interaction became necrotrophic with collapsed host cells. Quantitative differences in appressorium formation and host colonization were found between the two almond cultivars studied. Thus, on the less susceptible cv. Nonpareil fewer appressoria developed and host colonization was reduced compared with that on cv. Carmel. 相似文献
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Hernández-Salinas Gregorio Luna-Cavazos Mario Soto-Estrada Alejandra García-Pérez Eliseo Pérez-Vázquez Arturo Córdova-Téllez Leobigildo 《Genetic Resources and Crop Evolution》2022,69(1):99-116
Genetic Resources and Crop Evolution - Carica papaya L. is an important plant genetic resource that has a low level of genetic erosion. Knowing the distribution and eco-geography of native C.... 相似文献
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