Solanum nigrum, a new host for powdery mildew disease of Capsicum annuum in the Madurai district of Tamil Nadu, India
In October–November 2004, a severe outbreak of powdery mildew disease incited by Leveillula taurica was observed on Capsicum annuum (cv. K2) (chilli) and caused yield loss up to 80%. A similar type of symptom was also recorded on Solanum nigrum grown in and around chilli fields. Based on the morphological characteristics and cross infectivity, it has been confirmed that the powdery mildew pathogens from C. annuum and S. nigrum are the same. The pathogen from C. annuum could infect S. nigrum and vice versa. Other cultivated plant species were not infected. This might be due to the probable occurrence of physiological races. This is the first report of this organism causing powdery mildew in S. nigrum in the Madurai district of Tamil Nadu. The ability of L. taurica to infect the native host S. nigrum is particularly important because this host plant might serve as an inoculum reservoir for adjacently cultivated C. annuum.
First Report of Powdery Mildew of Greenhouse Pepper Caused by Leveillula taurica in Canada.
In 1999, powdery mildew on cvs. Oberon and Triple 4 of greenhouse pepper (Capsicum annum L.) and cv. FireFlame of chili pepper was reported simultaneously in two commercial greenhouses at two separate locations, Leamington and Vineland, geographically separated by 290 km, in southern Ontario. Losses of 10 to 15% each in the 2 and 3.1 ha greenhouse pepper operations were noted. The greenhouse pepper industry in Canada consists of 89.4 ha with sales of $43.6 million (Canadian). Lesions appeared as a white, powdery coating on the abaxial leaf surface only, generally on the lower foliage of pepper plants, while diffuse chlorotic spots were present at corresponding locations on the adaxial surface. In chili pepper, this chlorosis was restricted to interveinal tissue, causing the leaves to have a somewhat netted appearance. In some cases, pale yellow spots appeared on the adaxial portion of the affected foliage during later stages of disease development. No cleistothecia were observed. Pyriform and cylindrical, hyaline, single-celled conidia were present in equal numbers. Both conidia had a network of crests and granules containing tiny, thornlike projections on the surface. These projections were also evident on the lower half of conidiophores. Pyriform conidia ranged in length from 61.6 to 84.0 μm (mean = 70.8, SE = 0.7) and in width from 14.0 to 25.8 μm (mean = 21.1, SE = 0.4, n = 50), with a mean length to width ratio of 3.4. Cylindrical conidia ranged in length from 54.9 to 80.1 μm (mean = 66.3, SE = 0.9) and in width from 15.7 to 24.1 μm (mean = 18.6, SE = 0.3, n = 50), with a mean length to width ratio of 3.1. Short conidial chains borne on conidiophores consisted of a pyriform conidium first followed by cylindrical conidium. Stomatal penetration and extensive endophytic mycelial growth in the mesophyll layer were evident in foliar tissue cleared with glacial acetic acid:EtOH (1:2) and stained with lactophenol cotton blue. To confirm pathogenicity, conidia from infected pepper leaves were dusted onto the water-misted abaxial leaf surface of 41-day-old greenhouse pepper cvs. Cubico and Edison, and onto the similarly treated adaxial leaf surface of 58-day-old field pepper cv. Renegade. Plants were enclosed in plastic bags for 24 h on a bench. Control plants were treated identically but not inoculated. Inoculated plants developed foliar powdery mildew symptoms, including sporulation similar to that of naturally infected plants. Occurrence of the fungus on the abaxial surface of pepper foliage, presence of endophytic mycelium, and the morphological characteristics of the imperfect state confirm the identity of the fungus. This is the first report of Leveillula taurica (Lév.) G. Arnaud on pepper in Canada. Reference: J. Palti. Bot. Rev. 54:423, 1988.
Some observations on Erysiphe Polygoni DC.
Summary 1. In field trials in 1913 no variety, out of seventy-seven varieties of Swedes, Turnips and Rape, was found to be immune to Erysiphe Polygoni DC. Swedes were attacked more severely than Turnips. 2. In inoculation experiments with cultivated varieties of Brassica campestris and B. oleracea , the form of Erysiphe Polygoni infecting these varieties was found to be a “biologic form” with this additional distinction that inoculations from B. campestris to B. oleracea invariably gave “subinfections” as the result. 3. “Biologic forms” on Polygonum aviculare, Trifolium Pratense and Pisum sativum were indicated. 4. “Subinfections” on varieties of B. oleracea were observed in the field and found to exist over the winter and in some cases grow into full infections. 5. Inoculations were undertaken in the laboratory and were successful both on uninjured leaves and on the internal tissues of stems; these latter were carried as far as the fourth generation. 6. Inoculationswithconidiafrom “subinfections” werecarried out and the conidia shown to be viable. 7. It is suggested that the most probable method of overwintering of the “biologic form” of Erysiphe Polygoni on the cultivated Brassicae is by means of “subinfections” on varieties of B. oleracea aided by persistent mycelium on varieties of B. campestris .