13. Allelism test between Pl-i and pl2(t) responsible for purple leaf in rice

T. KINOSITA

Professor Emeritus, Hokkaido University, Sapporo, 060 Japan

According to the comprehensive study of anthocyanin coloration, it was elucidated that the basic coloration genes, C, A and P estimated from apiculus color are responsible for tissue-specific anthocyanin coloration together with several kinds of distributing genes and their suppressors (Kinoshita 1984). As for the leaf coloration, the four alleles of Pllocus interact with the high rank of basic genes as follows:

Pl Leaf blade, leaf sheath, collar, auricle, ligule, node and internode.

Pl-w Leaf blade, leaf sheath, auricle, ligule, a part of collar and node, internode and pericarp.

Pl-i Leaf blade, leaf sheath, ligule, and internode except collar, node and auricle.

Pl+ null allele resulting in colorless phenotype.

Besides that, six kinds of inhibitors, IPl1-IPl6 exert their action corresponding to the different

alleles of Pl locus.

Further, a new gene for purple leaf, pl2(t) was proposed by Sanchez and Khush ( 1994) and the trisomic analysis indicated that pl2(t) is located on chromosome 4.

In response to our request for material for an allelism test, Dr Khush kindly provided us with some seeds of a pl2 tester, R94-2672-4. First we noticed that the coloration of leaf organs in R94-2672-4 closely resembles our tester MA9553 which possesses the genotype of C-Bp, A, Pl-i, lg. MA9553 is a progeny from the cross involving I-102 fully purple (IRRI Ace. 100835). R94-2672-4 was then crossed with MA9553 as a male parent and F1 plants had the coloration pattern which was identical with those of both parents, and had normal ligule. In F2 population, all 616 plants exhibited the same coloration of leaf organs. In contrast to this, presence and absence of ligules segregated into 463 and 153, respectively in the same population showing a fitness to the 3:1 ratio for lg 2=0.009, p>0.9). Therefore, it was demonstrated that both parents have same genotype for anthocyanin coloration.

In a previous report (Kinoshita and Maekawa 1986), we found that both Pl-i and IPl6 are responsible for the coloration of leaf blade and sheath in the crosses involving I-102. A suppressive effect of IPl6 is restricted only for Pl-i and inhibits completely the coloration of leaf blade and sheath indistinguishable with normal green plants. From the crosses with japonica testers, the inhibitory ratio was calculated from the fact that F2 segregation fits the 3 purple : 13 green and the progenies of purple F2 plants segregated into 3 purple: 1 green besides purple progenies bred true. Moreover, a monogenic segregation was also confirmed in the F2 population from the cross, I-32 Kasalath/I-102 and the genotype of I-32 was estimated as Pl-i IPl6. As a result it is supposed that there are three genotypes, Pl-i IP16, + IP16 and + + showing green plants.

In this allelisrn test, it was difficult to decide whether pl2(t) is identical with Pl-i or if pl2(t) corresponds to a recessive state of IPl6. Because pl2(t) is located on chromosome 4, it is highly plausible that pl2(t) is identical with Pl-i and the inhibitor ratio due to IPl6 and Pl-i was overlooked as a single gene recessive.

Recently, Reddy et al. (1995) described the biosynthetic pathway of anthocyanin pigmentation depending on tissue-specific accumulation of anthocyanins due to the presence of a different set of Pl alleles. As the coloration trait can be effectively used as a marker for selection in both conventional and hybrid rice breeding, both classical and molecular genetic information is useful.

The author is greatly indebted to Dr. M. Maekawa, Research Institute for Bioresources, Okayama University for his assistance.

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References

Kinoshita, T., 1984. Gene analysis and linkage map. In Biology of rice. S. Tsunoda and N. Takahashi eds. pp. 187-274. JSSP/Elsevier. Tokyo.

Kinoshita, T. and M. Maekawa, 1986. Inheritance of purple leaf color found in Indica rice. Jour. Fac. Agric., Hokkaido Univ. 62:453-466

Reddy, V.S., S. Dash and A.R. Reddy. 1995. Anthocyanin pathway in rice (0ryza sativa L.): identification of a mutant showing dominant inhibition of anthocyanins in leaf and accumulation of proanthocyanidins in pericarp. Theor Appl Genet 91: 301-312.

Sanchez, A.C. and G.S. Khush, 1994. Chromosomal location of some marker genes in rice using the primary trisomics. J. Hered. 85: 297-300.