Primary trisomics in Moss Verbena

Abstract

Four, out of the maximum of 5 possible, primary trisomics have been identified karyomorphologically. These are Pseudo Normal, Slender, Semi Erect and Weak, trisomic for C, A, B and D chromosomes respectively. The trisomics are reasonably distinguishable from one another on the basis of qualitative and quantitative characters, like growth habit and rate, stem thickness, internode length, size and shape of leaves and flowers and fertility. The most common type of association at meiosis is 5II+1 I followed by 1 III+4 II. The trisomics differ in the number and type of trivalents. There is a significant increase in range and number of ring bivalents in all trisomics particularly in Slender. This is attributable to a correspondingly significant increase in chiasma frequency. The reasons for this are not clear. Anaphase segregation is ordinarily normal and pollen fertility is high except in Semi Erect in which it is correlated with segregational errors. Although, seed setting is apparently normal in all except Slender, yet germinability is very poor. Greater phenotypic effects and lesser tolerance to the addition results in trisomics for the long submedian and satellited A and medium submedian D chromosomes than for B and C chromosomes.