Development of ovule, megagametophyte and early endosperm in representative species of Rhododendron L. (Ericaceae)

PALSER, B. F., PHILIPSON, W. R. & PHILIPSON, M. N., 1989. Development of ovule, megagametophyte and early endosperm in Rhododendron L. (Ericaceae). Complete development of ovule, megagametophyte and early endosperm is compared for 15 species (almost complete for four additional species) representing all subgenera and most sections of Rhododendron. In all the ovule is anatropous, unitegmic, tenuinucellate with the lateral and micropylar nucellus disintegrating completely. The integument has a tanniniferous epidermis, starch around egg apparatus and micropyle, an endothelium and hypostase. Differences occur in time of closure of the micropyle and its final length, total proportion of ovule occupied by gametophyte and by formation of ovule tails only in section Vireya. Megagametophyte development follows the Polygonum pattern in all species. A single archesporial cell becomes the megaspore mother cell directly, and the chalazal spore of a linear tetrad functions. Between the eight-nucleate stage and maturity the micropylar end of the gametophyte elongates into the micropyle. Starch is characteristically present in the mature central cell. The pollen tube penetrates porogamously and double fertilization is rapid. Endosperm development starts promptly and is cellular, first forming a linear row of four cells. The zygote elongates slightly but does not divide during the stages followed. Differences may occur in time of enlargement, orientation of some mitoses, some cellular characteristics, amount of starch present and final size of megagametophyte. Rare abnormalities occur.     

The combined use of mineral oils and pyrethroids to control plant viruses transmitted non- and semi-persistently by Myzus persicae

A mixture of the pyrethroid WL85871 (an enriched form of cypermethrin) and the mineral oil SC811 intoxicated adult apterae of an insecticide-susceptible clone of the peach-potato aphid Myzus persicae at a similar rate to a treatment containing only WL85871, but the mixture killed more. Mixtures of WL85871 andSC811 also gave better control of both acquisition and inoculation by M. persicae of the non-persistent potato virus Y (PVY) than either component alone. A mixture of the pyrethroids deltamethrin, cypermethrin and PP321 with SC811, or a mixture of WL85871 with the mineral oil Bayol 52 also decreased acquisition of PVY, and a mixture of WL85871 with SC811 decreased acquisition of another non-persistently transmitted virus, beet mosaic virus. Control with mixtures was generally better than that provided by each component applied separately. When testing acquisition or inoculation of the semi-persistent beet yellows virus, fewest plants were infected in treatments incorporating both WL85871 and SC811.