Infection of onion leaves by Alternaria porri and Stemphylium vesicarium and disease development in controlled environments

Abstract

Infection of onion by Alternaria porri and Stemphylium vesicarium was investigated under a range of controlled temperatures (4±258C) and leaf wetness periods (0±24 h). Conidia of A. porri and S. vesicarium germinated within 2 h when incubated at 48C. Terminal and intercalary appressoria were produced at similar frequencies at or above 108C. The maximum number of appressoria was produced after 24 h at 258C. Penetration of leaves by both pathogens was via the epidermis and stomata, but the frequency of stomatal penetration exceeded that of epidermal penetration. There was a strong correlation (R 2 . 90%) between appressorium formation and total penetrations at all temperatures. Infection of onion leaves occurred after 16 h of leaf wetness at 158C and 8 h of leaf wetness at 10±258C, and infection increased with increasing leaf wetness duration to 24 h at all temperatures. Interruption of a single or double leaf wetness period by a dry period of 4±24 h had little effect on lesion numbers. Conidia of A. porri and S. vesicarium separately or in mixtures caused similar numbers of lesions. Alternaria porri and S. vesicarium are both potentially important pathogens in winter-grown Allium crops and purple leaf blotch symptoms were considered to be a complex caused by both pathogens.

Field Management of Taro Leaf Blight using Promising Germplasm of Taro

“…The disease was thus rapidly increased in terms of PDI values. The results are also corroborated with the earlier work of Suheri and Price (2000) and Razdan et al, (2008). Severity of the blight depends on the favourable in environmental factor, availability of inoculums and stage of plant growth and time of disease appearance The disease incidence in general continued to increase day by day which might directly be correlated with the epidemiological parameters as there were a subsequent increase in highest relative humidity (RH I), lowest relative humidity (RH II) and rainfall (Table 3).…”

“…Muktakeshi and BCC-1 are the tolerant cultivars, which showed low PDI at suitable epidemiological environment. Razdan et al, (2008) and Suheri and Price (2000) results are agreed with the earlier work.…”

Pathogens Associated with Foliar Blight of Onion

“…The results of the present study are in conformity with Jakhar et al (1996) who reported that the disease caused by Stemphylium first increased gradually, and then decreased late in the season. The results of the present study revealed that the symptoms of A. porri and S. vesicarium were indistinguishable in the field, which is in conformity with the results of Suheri and Price (2000) who reported that typical purple blotch lesions in the field were often colonized by both the pathogens. Aveling et al, (1993) showed that S. vesicarium, in conjunction with A. porri, was a destructive foliar and seed stalk pathogen of onion under warm, moist conditions.…”

“…Dennis (leaf rot or blast), and Stemphylium botroysum. Suheri and Price (2000) reported that both A. porri and S. vesicarium were potentially important pathogens of winter grown Allium crops and purple leaf blotch symptoms were considered to be a complex caused by both the pathogens. Stemphylium botryosum (Pleospora herbarum), S. vesicarium and Alternaria alternata were isolatedin 93.7, 12.5 and 50.0 per cent of the samples, respectively (Cova and Rodriguez, 2003).…”

Host range and phytotoxicity of Stemphylium solani, causing leaf blight of garlic (Allium sativum) in China

“…Stemphylium vesicarium and A. porri are the pathogens most frequently reported on the diseased leaves of garlic. These two pathogens can both cause white or purple spots of onion, and both can be present in the same spots and cause the same level of disease on onion (Suheri and Price 2000b).…”