Reasons why BC15 rice variety has empty grains.

(Baonghean)This winter-spring season, thousands of hectares of BC15 rice in Nghe An, Thanh Hoa, and Vinh Phuc provinces suffered from empty grains. On May 21st, the Department of Crop Production (Ministry of Agriculture and Rural Development) held a meeting with scientists and local authorities to determine the cause and discuss timely solutions. The meeting concluded that the empty grains in BC15 rice are due to the variety's biological sensitivity to unfavorable weather conditions. For more details, we present the article "Causes of Empty Grains in BC15 Rice" by engineer Doan Tri Tue.

To understand and clarify the reasons why the BC15 pure rice variety supplied by Thai Binh Seed Corporation, when planted in Nghe An, suffers from empty grains, while other rice varieties planted and cared for in the same way do not experience such severe empty grains as BC15, we would like to mention three major drawbacks that easily lead to risks for producers:

- Rice blast disease is very common during the spring season.

- Highly sensitive to low temperatures and poor at tolerating cold. Therefore, in the spring, if the air temperature drops below 18°C, seedlings and newly transplanted rice are very susceptible to mass die-offs.

- Cracked rice grains: This is a major drawback inherited from generation to generation that cannot be overcome. Its origin is from the IR17494 (13/2) rice variety, which was widely cultivated in Nghe An province from the late 1990s and early 2000s. Because of this drawback, farmers in Nghe An commonly call it "cracked rice" or "split rice." After harvesting, even with good storage, the rice grains are still susceptible to weevils.

So what are the underlying reasons why BC15 rice has so many empty grains?

Most BC15 rice varieties that flowered between April 23rd and 28th had a 60-70% empty grain rate. Other varieties, similar to BC15 but flowering earlier, yielded an average of 70-75 quintals/hectare and flowered around the same time (April 23rd-28th), without this problem. Of the three major drawbacks mentioned above, two contributed to the high number of empty grains in this year's spring crop:

The BC15 rice variety is inherently less tolerant of cold compared to all other pure rice varieties currently grown in Vietnam. A large portion of the BC15 rice crop that flowered between April 23rd and 28th suffered from 60-70% empty grains. Considering the flowering period, the average air temperature was 27.1°C, the average maximum air temperature was 31.2°C, and the average minimum air temperature was 24.6°C. Such air temperatures did not affect the rice flowering. However, looking back at the days before flowering, it shows that from April 7th to 14th, 2013, there were successive cold fronts, causing air temperatures to drop below 17°C and 18°C, and on April 12th, 2013, the air temperature dropped below 17°C. This period coincides with the 5th-6th stage of panicle differentiation in the BC15 rice variety, which is heavily damaged. For the BC15 rice variety, if the air temperature drops below 20°C during the panicle differentiation stage, it significantly affects the development of the rice flower, causing the stamens to become short, small, and shriveled, the pollen grains to degenerate, and the plant's vitality to decrease.

Therefore, after the rice has finished flowering, we will see many empty or partially filled grains on the rice panicle, and the end of the panicle is severely degenerated, failing to form rice grains.

The fact that 60-70% of the BC15 rice variety's grains were partially empty also has another very important cause: heavy rain and strong winds during the rice flowering period. While other rice varieties were unaffected, only the BC15 variety suffered heavy losses because its two husks do not close completely.

For rice plants, when flowering, if they encounter unfavorable weather conditions such as severe cold, overcast skies lacking sunlight, strong winds and rain, excessively hot sun, or excessively high air temperatures, the two husks of the rice flower will automatically close to protect the stamens and pollen. However, with the BC15 rice variety, although both husks close, they are not completely sealed. Therefore, during heavy rain and strong winds, some of the stamens and pollen are washed away by the rainwater, while others are blown away by the strong winds. According to meteorological and hydrological data, on April 24th and 26th, 2013, the Dien-Yen-Quynh region experienced two heavy rainstorms with strong winds (rainfall measured in Quynh Luu was 43.7mm and 86mm), precisely when the BC15 rice variety suffered significant damage, flowering, and pollination. Other rice varieties that flowered before or after these times still yielded normal, high rice productivity.

Based on the above monitoring, analysis, and evaluation results, it can be confirmed that the reason for the high percentage of empty or partially filled grains in BC15 rice during this year's spring crop, reaching 60-70% in some areas, is not due to poor seed quality but mainly due to unfavorable weather conditions during the panicle differentiation stages (stages 5 and 6) and the flowering and tillering stages, as mentioned above.

Doan Tri Tue