Rao, R. N., and Panuganti N. Rao A chromosomal variation associated with susceptibility to lady bird beetle.
In M1 generation of gamma-ray treated tomato cv. Marglobe, one plant had an extra small chromosome and
a translocation complex of 4. The chromosomes involved in translocation could be arbitrarily numbered as 1.2, 2.3,
3.4 and 4.1. The chromosome 4.1 was conspicuously small and was believed to be deficient for a large
heterochromatic segment. The extra chromosome, which was smaller than 4.1, formed together with these 4
chromosomes a ring of 5 in some plants in subsequent generations, and it was considered to be an isochromosome
for the short arm having little heterochromatin. It was designated as 3.3. The plants in M2, M3 and M4 generations
showed a wide array of genomic constitutions and segregated for susceptibility to lady bird beetle (Henosepilachna
vigintioctopunctata). The segregation did not, however, follow any set pattern. Compared to the normal resistant
plants, the susceptible ones had smaller dark green glossy leaves with an uneven surface and there was a marked
decrease in number of trichomes (both uni- and multicellular) per unit area and considerable numbers of glandular
hairs (with tetrahedral heads) were present an the leaf surface. The cytogenetic analysis revealed that the
susceptibility is governed by a dominant mutation arising during the course of the reciprocal exchange of segments
between nonhomologous chromosomes. The lack of clear-cut monogenic segregations was believed to be due to
preferential pairing of chromosomes (1.2, 1.2) in certain constitutions (1.2, 1.2, 3.4, 1.4, 3.3 in the following
situation, where, as frequently observed, pairing occurred as a bivalent and heteromorphic trivalent). The
chromosomes were directly oriented at meiosis (1.4 and 3.3 in the trivalent going to the same pole frequently); the
abnormal gamete (with 1.4 and 3.3) segregated
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