Necrotic Leaf Lesions Research Articles

Pythium tracheiphilum . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Pythium tracheiphilum . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Lactuca saliva, Spinacea oleracea . DISEASE: Vascular wilt and stem rot of lettuce; a facultatively necrotrophic plant pathogen. Symptoms are severe stunting and wilting of young or maturing plants, vascular browning and necrotic leaf lesions, which may be large or small and restricted (58, 2495). GEOGRAPHICAL DISTRIBUTION: Europe; Germany, Italy, Netherlands, Sweden, UK (England). North America: USA (WI). TRANSMISSION: Presumably by zoospores in moist soil and by rapid mycelial growth. Oospores and resting spores probably act as perennating structures.

Phoma epicoccina . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Phoma epicoccina . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS AND SUBSTRATA: Avena seeds, Beta vulgaris, Dacrylis glomerata, Malus sp., Phaseolus sp., Triticum sp., Zea mays , air and straw decaying in soil. DISEASE: Information on pathogenicity is still unclear, but according to Herb. IMI records P. epicoccina has been isolated from necrotic leaf lesions in the Irish Republic and also in UK. It is a common contaminant of grass seeds (Tulloch & Leach, 1972) and beet seed. As the Epicoccum state of P. epicoccina is indistinguishable from Epicoccum nigrum Link (= E. purpurescens Ehrenb. ; CMI Descriptions 680) it is possible that the former could be confused with the latter. From the available data, P. epicoccina could be regarded as a saprophyte or a weak pathogen. GEOGRAPHICAL DISTRIBUTION: Asia (India); Australasia (New Zealand); Europe (France, Irish Republic, Netherlands, Sweden, UK); North America (Canada, USA, Oregon). TRANSMISSION: The Epicoccum state has been isolated from air and also commonly associated with orchard grass seed (Tulloch & Leach, 1972). Conidia are presumably dispersed by air and also seed-borne.

Response of Petunia Plants to SO2 and of Detached Leaves, Leaf Discs, and Callus to Sodium Sulfite1

Abstract Flowering plants of 5 cultivars of petunia (Petunia hybrida Vilm.), exposed to 2.8 ppm SO2 (16 hours) under controlled environmental conditions, exhibited variation in SO2 sensitivity based on the degree of water-soaked necrotic leaf lesions. The range of SO2 absorption rates was ± 14% of the mean for the 5 cultivars; however, there was a 2-fold difference in sensitivity among the cultivars, indicating that variation in SO2 absorption plays only a limited role in determining the genetic differences involved in the reaction of petunia to SO2. Detached leaves from all cultivars were equally sensitive to a 10 mM Na2SO3 solution. The injury response of leaf discs to Na2SO3 solutions was monitored by chlorophyll extracts. Although the cultivars varied in sensitivity, the ranking differed from that observed for whole plants to SO2. Callus cultures grown on Murashige and Skoog (MS) medium + naphthaleneacetic acid (NAA) at 2.0 mg/liter + ben-zylamino purine (BA) at 0.5 mg/liter were treated with Na2SO3. Their viability, when evaluated by triphenyl tetrazolium chloride (TTC), yielded a sensitivity ranking of the same cultivars which differed from that obtained with both leaf discs and whole plants. No differences in Na2SO3 sensitivity were observed for callus cultures of the cultivars cultured on MS + 1.0 mg/liter 2,4-dichlorophenoxyacetic acid (2,4-D). The dissimilar injury responses to SO3=/HSO3 − in different tests on explants of the same cultivars indicate that at each level of plant organization sensitivity to Na2SO3 is determined by different morphological and physiological factors from those which specify whole plant reaction to SO2.