College of Agriculture and Animal Science, Yeungnam University,Kyeongsan, Korea
Weedy forms of rice are found in rice fields in many rice growing countries. They propagate themselves by naturally shed seeds or by being harvested and sown together with cultivated rice (Oka 1988). The weed rice can provide not only information useful for understanding the evolution of rice, but also germplasms tolerant to adverse conditions for rice breeding. Weed rices are found in many rice fields in Korea. They are characterized by red pericarp and are called "red rice", although a few of them are colorless.
A large number of plants of the red rice were collected from all over South Korea for examination of their character variation. They were classified into "long-grain" and "short-grain" types, as intermediate grain types were few. The long-grain type were obtained only from southern regions of the peninsula, while the short-grain types were distributed throughout the country (Fig. 1 Suh et al. 1992).
Fig. 1. Regional distribution of weed rices of long- and short-grain types
in Korea.
The grain-shape variation was not correlated with phenol reaction, although plants with negative reaction were more frequent in the long-grain than in the short-grain types (Table 1). Some of the short-grain plants were glutinous, but all long-grain plants were non-glutinous. Also, about half of the short-grained plants were awned, but awned long-grain plants were rare (Table 1). Most of the weed rices shattered grains easily, although some of short-grained plants had normal threshability.
The long-grain and short-grain types showed no significant differences in panicle length, grain test weight, seed fertility, amylose content and alkali digestibility of the endosperm (Table 1, lower part). But they differed in culm length, panicle number per hill, and spikelet number per panicle.
To examine F`1`-sterility relationships, 7 long-grain and 5 short-grain lines were crossed with two Indica (IR26 and IR50) and two Japonica (Geumobyeo and Shin 2) testers, respectively. The F`1` plants of long-grain types with Indicas had 78% pollen and 48% seed fertilities, and those with Japonicas had 37% pollen and 27% seed fertilities, on the average (Table 2). The F`1` plants of short-grain types with Indicas had 41% pollen and 37% seed fertilities, and those with Japonicas had 68% pollen and 59% seed fertilities. These results suggest that the long-grained weed rices are closely related to the Indica and the
Table 1. Characters of Korean weed rices classified into long-grain and short-grain types _______________________________________________________________________________ Long-grain Short-grain No. of strains Character type % type % observed _______________________________________________________________________________ Pericarp color, Red to brown 90.8 99.4 1130 Colorless 9.2 0.6 Phenol reaction (hull & pericarp), Positive 9.3 30.7 853 Negative 90.7 69.3 Endosperm characters, Ordinary 100 95.7 1103 Glutinous 0 9.3 Awn,presence or absence, Awned 2.4 49.6 1105 Awnless 97.6 50.4 Grain shedding, Easy 100 85.2 1103 Normal 0 14.8 Metric character, mean+/-standard Long- & short-grain deviation Difference _______________________________________________________________________________ Culm length, cm 104 +-7.5 95 +-10.5 ** Panicle length, cm 22.1+-1.6 22.3+-2.0 ns No. of panicies/hill 21.5+-4.5 11.8+-2.7 ** No. of spikelets/panicle 86 +-25.3 109 +-24.8 ** 1000-grain weight, g 20.1+-2.4 20.2+-1.8 ns Seed fertility, % 80.4+-8.9 79.4+-9.5 ns Amylose content, % 31.7+-3.0 27.1+-5.0 ns Alkali digestibility 7.0+-1.4 7.4+-2.1 ns _______________________________________________________________________________ ** Difference between long- and short-grain types being significant at 1% level ns Non-significant
Table 2. Pollen and seed fertilities of F`1` plants of Korean weed rices crossed with Indica and Japonica test-strains _______________________________________________________________________________ Indica testers Japonica testers Strain group Pollen Seed Pollen Seed _______________________________________________________________________________ Long grain Mean 78% 48% 37% 27% Max. 90 79 65 55 Min. 72 42 25 5 Short grain Mean 41 37 68 59 Max. 87 51 86 73 Min. 24 20 42 44 _______________________________________________________________________________short-grained weed rice are closely related to the Japonica cultivars. Five short-grained lines were crossed with two long-grained lines to observe the hybrids between short and long-grained red rices. The results showed that the F`1` pollen fertilities were 50% to 79% with a mean of 60% and the F`1` seed fertilities were 35% to 64% with a mean of 50%.
References
Oka, H. I., 1988. Weedy forms of rice. In Origin of Cultivated Rice, p. 107-114. Elsevier/Japan Sci. Soc. Press, Amsterdam/Tokyo.
Suh, H. S., S. Z. Park and M. H. Heu, 1992. Collection and evaluation of Korean red rices, 1. Regional distribution and seed characteristics. Korean J. Crop Sci. 37: 425-430. (in Korean)