From herkogamy to cleistogamy--development of cleistogamy in periwinkle.

Periwinkle (Catharanthus roseus [L.] G. Don), an important medicinal plant, is an allogamous species in which the stigma is below the anthers. The receptive portion is at the base of the stigmatic head and thus automatic intra-flower self-pollination is excluded. The structure of the flower is of typical reverse herkogamy and pollination occurs through nectar-seeking insects. A few self-pollinating strains are also reported in which self-pollination is brought about by an increase in length of the style or of the ovary. Self-pollination is governed by allelic duplicate genes recessive to allogamy. An induced monogenic recessive mutant (EMS 17-1) with caducous closed corolla (corolla abscising before anthesis), isolated from variety, Dhawal, was crossed with two self-pollinating strains to study the possibility of obtaining cleistogamous recombinants combining closed corolla and self-pollination traits. Cleistogamous plants were obtained in which development of fruits and seeds occurred without opening of the corolla. Closed corolla and self-pollination were found to be independently inherited. A dominant gene in the parent in which self-pollination occurred due to an increase in length of the ovary, appeared to completely or partially inhibit expression of the gene for closed corolla in homozygous or heterozygous condition, respectively. The genetic basis of development of cleistogamy is described. Cleistogamy in periwinkle would facilitate in ensuring genetic purity, pollen containment, and seed production even in the absence of pollinators. This appears to be the first report on the development of cleistogamous plants in an allogamous species.

A somaclonal variant of rose-scented geranium (Pelargonium spp.) with moderately high content of isomenthone in its essential oil.

Rose-scented geranium (Pelargonium spp.), which is highly valued for its essential oil, is exclusively propagated vegetatively. Hence no genetic improvement work is possible through conventional breeding. Somaclonal variation was generated with and without in vitro mutagenesis using N-nitroso-N-methyl urea (NMU) in an Indian cultivar 'Bourbon', and a clone 'Narmada'. A somaclonal variant (N75) with a moderately high content of isomenthone in its essential oil was isolated from somaclones generated after treatment of internodal explants of clone, 'Narmada' with 0.25 mM NMU for 1 h. The contents of isomenthone in its essential oil were 26% and 35%, respectively, in SC2/VM2 and SC3/VM3 generations (second and third vegetative generations, respectively, after in vitro mutagen treatment) as compared with 0.7% and 0.3%, respectively, in the parental clone, 'Narmada'. The contents of alcohols and their esters (linalool, citronellol, geraniol, citronellyl formate and geranyl formate) in the essential oil of N75 in SC2/VM2 and SC3/VM3 generations were 49% and 35%, respectively, as compared with 69% and 63%, respectively, in the parental clone, 'Narmada'. This is the first report on a chemovariant of rose-scented geranium with a moderately high content of isomenthone. All earlier reported isomenthone-rich variants of rose-scented geranium had quite high contents of isomenthone (64-71%) in their essential oils. The probable modes of origin of this somaclonal variant, its parental clone 'Narmada' (with very low content of isomenthone) and four earlier reported isomenthone-rich variants of Indian cultivars of geranium are discussed.