FURTHER OBSERVATIONS ON THE DIFFERENTIAL SENSITIVITIES TO PLANT GROWTH REGULATORS BY CULTURED “SINGLE” AND “DOUBLE” FLOWER BUDS OF NIGELLA DAMASCENA L. (RANUNCULACEAE)

In Nigella damascena, where “doubleness” behaves as a single gene character, recessive to the normal wild “single” form, we detected a number of differential responses of cultured floral apices of the two forms to plant growth regulators. “Single” buds initiated all organ types on a defined medium lacking any plant growth regulators. “Double” buds, however, required either kinetin or GA₃ for the development of a normal organ complement. Kinetin enhanced the growth and development of buds of both genotypes, whereas GA₃, at all concentrations, specifically inhibited the initiation and growth of stamens and nectaries in “single” buds. No combination of IAA or kinetin overcame this inhibition of “single” buds by GA₃. In the presence of both IAA and GA₃, “single” buds, following the initiation of normal carpels, initiated a few abnormal carpelloid structures from regions which had failed to produce stamens and nectaries. These observations, coupled with other studies including those on the endogenous levels of gibberellin in the two genotypes, suggest that “doubleness” correlates strongly with a modification of gibberellin metabolism. The causal connection between the two phenomena is as yet to be discovered.     

CYTOGENETIC STUDIES ON THE ORIGIN OF TAGETES PATULA. I. MEIOSIS AND MORPHOLOGY OF DIPLOID AND ALLOTETRAPLOID T. ERECTA × T. TENUIFOLIA

Towner , Joseph W. (U. California, Los Angeles.) Cytogenetic studies on the origin of Tagetes patula. I. Meiosis and morphology of diploid and allotetraploid T. erecta × T. tenuifolia. Amer. Jour. Bot. 48 (9): 743–751. Illus. 1961.—Cytological and morphological evidence is presented to show that Tagetes patula L. is an allotetraploid species (2n = 48) which probably originated by hybridization between the diploids T. erecta L. and T. tenuifolia Cav., or species closely related to them. The putative parent species are separated by strong reproductive isolation barriers, and controlled crosses between them yielded very few good seed. Most of the hybrid seedlings died before reproductive age, and the few survivors were sterile and extremely weak. At meiosis in the diploid hybrid, bivalent frequency per cell was 0–11 and averaged 4.4. Although 43.6% of the quartet stage consisted of restitution dyads, pollen was essentially all non-viable and seed set was less than 1%. A true-breeding, fertile, allotetraploid T. erecta-tenuifolia was synthesized by colchicine-doubling of the chromosome number of the F₁ hybrid. In the synthetic allotetraploid, average chromosomal association was 23.97 bivalents plus 0.05 univalents, and 97.4% of MI cells had 24 bivalents; there were no multivalents, bridges, or fragments. Tagetes erecta-tenuifolia showed a striking morphological similarity to T. patula. Both the natural and synthetic allotetraploids were intermediate between T. erecta and T. tenuifolia for nearly every character. Of 10 species of Tagetes whose chromosome numbers are known, 5 are tetraploid (2n = 48).     

COMPARATIVE DEMOGRAPHICS OF A GENERALIST PREDATORY LADYBIRD ON FIVE APHID PREY： A LABORATORY STUDY

Prey driven demographic parameters of an aphidophagous ladybird, Propylea dissecta (Mulsant) were studied in attempt to answer how ladybird overcomes the problem of seasonally fluctuating food base. The ladybird reared for five generations in laboratory derived differential nutrition from five food sources (i.e. aphid species, Rhopalosiphum maidis (Fitch), Aphis craccivora Koch, Aphis gossypii Glover, Uroleucon compositae (Theobald) and Lipaphis erysimi (Kalt.)). The order of relative prey suitability was A. gossypii, A. craccivora, R. maidis, U. compositae and L.erysimi. Neonates suffered maximum mortality followed by eggs. Estimates of net reproductive rate,intrinsic rate of increase and finite rate of increase were highest (407.18, 0.2274 day^-1, 1.2553 day^-1) on A. gossypii and lowest (176.02, 0.1533 day^-1, 1.1657 day^-1) on L. erysimi. Generation time was shortest (26.43 days) on A. gossypii and longest (33.73 days) on L. erysimi. The present study thus,provides an explanation to the high incidence of P. dissecta on A. gossypii, as it experienced high intrinsic rate of increase and optimal values for related demographic parameters.