5. Comparative gametic selection in sexual and anther culture derivatives of five rice hybrids

Plant breeding Department, International Rice Research Institute P. O. Box 933, Manila, Philippines, Present address: IRAT/CIRAD, BP 5035, 34032 Montpellier cedex, France

Aside from field evaluation, an accurate means to test the existence of gametic selection occurring during the androgenetic pathway is the comparative study of segregation of genetic markers among both sexual (F2 or backcross plants) and anther culture derivatives. In cultivated rice (Oryza sativa L.), the isozyme loci appear to be suitable markers for this purpose because of their high level of polymorphism in distantly related varieties (Glaszmann 1987) and their wide expression in anther culture derivatives (Gaiderdoni et al. 1988, 1989a).

In this study, segregation of 8 to 12 heterozygous isozyme markers was investigated among F2 Progenies and anther culture derivatives [non-morphogenic microspore-derived calli (NMC) and anther culture-derived plants (ACPs)] of 5 intervarietal hybrids. As shown in Table 1, the parental varieties belonged to the isozyme groups I (indica), V ("Basmati croup"), and VI (japonica) (Glaszmann 1987). Significant departures from the expected ratios were found at 1 to 5 isozyme loci among the F2 derivatives, indicating that in vivo gametic selection, which is most probably related to intervarietal F1 sterility, took place during gametogenesis. The alleles over-represented in the F\2\^S were generally found in excess in the NMC populations which, on the other hand, displayed further distortions at 1 to 4 loci depending on the hybrid used. These results suggest that non-morphogenic calli originate from a microspore pool that sustains both gametogenetic and androgenetic selections. However, neither the indica nor the japonica allelic types were favored at all the distorted loci by one or the other gametic selection.

As to the ACP populations, the segregation agreed with the expected 1: 1 ratio at all loci surveyed in IR64/Azucena (1 of 12 showed distorted segregation in the F\2\^S) and in Azucena/UP1Ri7 (5 of 8 markers displayed distorted segrega- tions in the F\2\^S). The morphogenic pathway of androgenesis seems therefore to avoid in vivo pollen selection which both affect segregation in NMC

Table 1. Segregation distortions of isozyme markers in F2 progenies, non-morphogenic calli (NMC) and anther culture plants (ACP) derived from five rice intervarietal F1 hybrids

b Mean value obtained in observing at least 15 panicles belonging to 5 F1 plants.

c Departure of the observed segregation from the expected 1: 2: 1 or 1: 3 ratio due to a disequilibrium in the calculated allelic frequencies, significant at least at the 5% level. Number of F2 plants analyzed: 178 to 420.

d Departure of the observed segregation from the expected 1 : 1 ratio among the anther culture derivatives, significant at least at the 5% level. Number of non-morphogenic calli analyzed: 139 to 399. Number of anther culture plants analyzed: 70 to 90.

e Whether ACP number is sufficient to carry on significant statistical analysis.

populations. In Azucena/UP1Ri7, anther culture bypasses the phenomenon of F1 hybrid sterility which hinders the exploitations of such crosses in rice breeding.

As these results contrast with the consistent segregation distortions observed in microspore derived-calli and doubled haploid lines derived from the japonical indica hybrid Irat177/Apura (Guiderdoni et al. 1989a, b), this study must be broadened to include other ACP populations to enable us to come up with generalizations. However, this apparent discrepancy may be explained by the existence (aside from the effect of F1 hybrid sterility) of another segregation distortion mechanism in our hybrids since segregation distortion of isozyme markers has been recently noticed in the F\2\^S of several intra-japonica F1 hybrids (M. Arraudeau, unpublished results). These mechanisms might interfere with gametogenesis at different levels and stages and consequently may or may not affect the morphogenetic pathway of androgenesis.

Glaszmann, J.C., 1987. Isozymes and classification of Asian rice varieties. Theor. Appl. Genet. 74: 21-30.

Guiderdoni, E., B. Delos Reyes and G. Vergara, 1988. Expression and segregation of isozyme genes in rice microspore derived calli. Int. Rice Res. Newsl. 13: 10-11.

Guiderdoni, E., B. Courtois and J. C. Glaszmann, 1989a. Use of isozyme markers to monitor recombination and assess gametic selection among anther culture derivatives of remote crosses of rice. In Mujeeb-Kazi, A. and L. A. Sitch, (eds.), Review of Advances in Plant Biotechnology, 1985-88: 2nd International Symposium on Genetic Manipulation in Crops.Mexico, D. F. and Manila, Philippines: CIMMYT and IRRI.

Guiderdoni, E., J. C. Glaszmann and B. Courtois, 1989b. Segregation of 12 isozyme genes among doubled haploid lines derived from a japonica/indica cross of rice. Euphytica 42: 45-53.