Comparison of tetraploid and single gene-induced gigas variants in chickpea (Cicer arietinum). I. Origin and genetic characterization.

Two genetic variants with increased organ size were independently derived from diploid (2n = 2x = 16) chickpea (Cicer arietinum L.) line ICC 640. Radiation-induced mutant PM 101 had greatly enlarged leaves, leaflets, and pods, and an elongated stem with longer intemodes but fewer nodes than ICC 640. F1, F2, and F3 data from crosses with ICC 640 showed that the mutant characteristics of PM 1 101 were the pleiotropic effects of a single, recessive genetic factor. For purposes of comparison, tetraploid derivatives of ICC 640 were produced by colchicine treatment of seed. In the tetraploids, leaflets and pods were enlarged, but less dramatically than in PM 1 101. Enlarged pollen grains and stomatal guard cells, and increased guard cell chloroplast number were found in tetraploids but not in PM 1 101, while both variants produced fewer seeds than ICC 640. Mutant PM 1 101 and the tetraploids represent two very different manifestations of gigantism in chickpea. INCREASED ORGAN SIZE has been an important component in the evolution of many cultivated plant species (Schwanitz, 1966). including chickpea (Cicer arietinum L.), an important food legume (Moreno and Cubero, 1978). Increases in organ or whole plant size may arise gradually via accumulation of small genetic changes, or suddenly via polyploidy or single gene mutation. A better understanding of the mechanisms by which specific genetic changes mediate well-defined effects on organ size will help plant geneticists guide the further evolution of crop plants in desired ways. We have initiated a study of how two well-defined genetic changes, polyploidy and single-gene mutation, lead to increased organ size in chickpea. The increased cell size associated with polyploidy in plants often produces thickened leaves and stems, enlarged leaves, fruits, and seeds, and other gigas characteristics (Stebbins, 197 1). In normally diploid (2n = 2x = 16) chickpea, reported effects of colchicine-induced tetraploidy include enlarged stomatal guard cells and pollen grains; enlarged seeds, leaflets and I Received for publication 31 October 1988; revision accepted 7 September 1989. Scientific Contr. No. 1589 from the Agricultural Experiment Station, University ofNew Hampshire, Durham, NH. The authors thank Brenda Giust for technical assistance on this project. 2 Current address: Dept. of Agronomy, University of Missouri, Columbia, MO 65211. 3 Correspondence and reprints. pods; thickened stems and leaflets; and darker green foliage (Bahl, 1987). Single-gene mutations conferring gigas characteristics have been reported in chickpea (Argikar, 1952; Chaudhari and Argikar, 1957; Athwal, 1963). A single-gene mutant with enlarged leaves, pods, and seeds was identified by Argikar (1952), and genetically characterized by Chaudhari and Argikar (1957). A similar gigas mutant, designated "Giant-I," had the normal, diploid (n = 8) chromosome number and no meiotic abnormalities (Athwal, 1963). As a by-product of an induced mutation study on root nodule formation (Davis, Foster, and Phillips, 1985), we have isolated a new chickpea mutant with markedly enlarged leaves, pods, seeds, and flowers. This mutant, number PM 1101, was derived from inbred parent ICC 640 via gamma-irradiation of seed (Davis et al., 1985; Davis, unpublished data). For purposes of comparison, we also have produced tetraploid derivatives of ICC 640. A comparative study of the anatomical and physiological characteristics of gigas mutant PM1 101, wild type parent ICC 640, and the tetraploid derivative of ICC 640 will provide insight into the mechanisms of genetic control over organ size. Differences among these three genotypes in respect to leaf anatomy are described in the accompanying report (Fagerberg, Davis, and Matthews, 1990). As a necessary prelude to this study, we describe here the inheritance of mutant PM 1101, the colchicine