3. Character variations of Korean weedy rice

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
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                                    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
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                 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
_______________________________________________________________________________

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)