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.
The morphology of the imperfect states of powdery mildews (Erysiphaceae)
In contrast to popular belief, a rich variety of morphological characteristics exists in the imperfect states of powdery mildews. Because it has been generally assumed that species cannot be distinguished by their appressoria, haustoria, conidiophores, conidia, fibrosin bodies, and conidial germ tubes, their morphology has received little attention and several older publications have even been forgotten. As with the perfect states, few species can be recognized by one characteristic of the imperfect state alone but many species can be identified when a combination of several characteristics is used. Important characteristics are the location of the mycelium, the production of conidia singly or in chains, the presence or absence of conspicuous fibrosin bodies, the appressoria, the size and shape of the conidia, and the position and type of their germ tubes. Many species are associated with particular families or genera of plants and therefore these are included in a key to identify 131 species of powdery mildew. This key shows how much and especially how little is known about many species. It is hoped that this review will stimulate study of the morphology of the imperfect states of numerous species. Consideration of both the perfect and the imperfect state should result in a more natural classification of several genera, for exampleUncinula andErysiphe which at present include both species which produce conidia in long chains and those which produce conidia singly.It appears that there are two lines of development of the imperfect states. One is characterized by lobed appressoria and conidiophores which produce conidia singly. The other is characterized by more or less rounded, unlobed appressoria and conidiophores which produce conidia in chains. A better knowledge of all the different imperfect states may provide more information regarding the evolution of powdery mildews.RésuméContraire à l’opinion commune, les stades imparfaits des Erysiphacées montrent une riche variété de caractéristiques morphologiques. Parcequ’en général on a supposé que les espèces ne peuvent pas être distinguées par leurs appressoria, haustoria, conidiophores, conidies, corpuscules de fibrosine et tubes germinatifs, leur morphologie a été étudié à peine et quelques publications anciennes ont même été oubliées. De même que les stades parfaits, on peut reconnaître peu d’espèces selon une seule caractéristique du stade imparfait mais beaucoup d’espèces en utilisant une combinaison de plusieurs caractéristiques. La localisation du mycélium, la production des conidies seules ou en chaînes, la présence ou absence de corpuscules de fibrosine bien visibles, les types d’appressoria, la grandeur et forme des conidies et la position et le type de leurs tubes germinatifs sont caractéristiques importantes. Plusieurs espèces sont associées avec des familles ou genres particuliers de plantes et donc les dernières sont présentées dans le clef d’identification de 131 espèces d’Erysiphacées. Ce clef montre au même temps combien est connu et combien est inconnu du stade imparfait.On espère que cette analyse stimulera la recherche de la morphologie des stades imparfaits de nombreuses espèces. Une considération des deux stades, parfaits et imparfaits, aurait pour resultat une classification plus naturelle. Par exemple les genresErysiphe etUncinula incluient espèces au conidiophores courts et aussi espèces au conidiophores longs. Il parait que les stades conidiens suivent deux lignes de développement. L’un des lignes est caractérisé par d’appressoria lobés et conidiophores produisant des conidies seuls; l’autre est caractérisé par d’appressoria plus ou moins arrondis, non lobés, et de conidiophores produisant des conidies en chaînes.Plus d’information sur les stades imparfaits contribuerait à la connaissance de l’évolution des Erysiphacées.
The Conidial Stage of Uncinula Necator
World collections of powdery mildew on grape are now generally recognized as Uncinula necator (Schw.) Burr. on the basis of the perithecial stage (5, 18). No basis of disagreement with the diagnosis will be presented here. Perithecia of Uncinula necator are commonly absent, however, and the fungus is usually known and identified on the basis of its conidial stage. This conidial stage shows great variation in different collections, though within a given collection and with collections at different times in a given locality, the conidial stage appears uniform. The purpose of this report is to document and discuss these variations.