Hybrid rice development is stalled: how can it be saved?

Data show that in recent years the downward trend in hybrid rice varieties has been very pronounced. The number of varieties with an annual promotion area of more than 1 million mu rose from 46 in 2002 to a peak of 59 in 2004, then declined year by year to 29 in 2012; the number of varieties with an annual promotion area of more than 5 million mu fell from about 9 in the early period to 1 per year at present; since 2007, no variety with more than 10 million mu has appeared. The average annual promotion area of a single main hybrid rice variety fell sharply from 2.133 million mu in 1993 to 374,000 mu in 2012, a drop of 82.5%.

“Save hybrid rice!” was the proposal heard most often by reporters on August 26 at the “C Liangyou Huazhan” upper Yangtze River variety demonstration meeting. In fact, as early as three years ago, Professor Chen Liyun of Hunan Agricultural University issued a call to save hybrid rice: saving hybrid rice should be treated as a major matter for solving our country's food security and rescuing the national seed industry.

“Saving hybrid rice is a systematic project, beyond the capacity of a few people or a few units. There must be policy support; the problems hindering hybrid rice development and the key technical solutions to those problems must be identified, and multidisciplinary collaborative innovation research must be carried out; close coordination among multiple departments and industries must be strengthened, so that under a top-level design framework each does its own part.” Chen Liyun said, “Only in this way will hybrid rice regain its youth.”

What is hindering development?

Former advantages have become disadvantages

In the past, the successful application of hybrid rice in our country was mainly attributed to its yield advantage (generally able to increase yield by more than 10%), seed price advantage (before 2008, hybrid rice seed price was below 12 yuan per kilogram), and seedling-raising technology advantage (the field seeding rate of hybrid rice was only 10%-20% that of conventional rice).

Today, with the continuous improvement of high-quality, high-yield conventional rice breeding, the yield gap between hybrid rice and conventional rice is narrowing. The yields of some high-yield conventional early rice varieties currently grown in production have approached the level of hybrid early rice; due to factors such as sharp rises in labor costs, high-price operations by seed companies, and high R&D costs for seed enterprises, hybrid rice seed prices have increased about 10-fold compared with the early period of development; with the rapid promotion of direct seeding and mechanical transplanting, seedling-raising and sowing densities are high, no tillering occurs during the seedling-raising period, and the seeding rate must be increased to ensure the basic number of seedlings, causing the field seeding rate of hybrid rice to multiply, which has led to a continuous reduction in hybrid rice planting area.

Lack of varieties suited to large-scale production

Direct seeding, mechanical transplanting, and mechanical harvesting are the main technologies of large-scale production. The greatest advantage of direct seeding is low cost, saving more than 200 yuan per mu; although mechanical transplanting costs about 100 yuan more per mu than direct seeding, grass weeds are easier to control, it can alleviate seasonal conflicts to a certain extent, and yield can be increased by extending the growth period of the variety, making it a key future development direction.

However, the biggest changes that direct seeding and mechanical transplanting require in hybrid rice traits are an increased field seeding rate and a shorter growth period. If it is wheat-stubble rice, the variety is usually required to have a growth period 5-10 days shorter than traditional transplanting; if it is double-season rice, early rice varieties are required to be early and medium maturing, and late rice varieties are required to have a growth period 5-8 days shorter than medium-maturing late rice varieties such as Wufengyou 308.

The biggest change that mechanical harvesting requires in hybrid rice traits is stronger lodging resistance, especially for direct-seeded rice. Once a variety lodges, in addition to yield and quality being affected, machinery cannot harvest it, and manual harvesting costs increase by more than 200 yuan per mu. The spread of mechanical harvesting and rising labor prices have made lodging resistance the first trait farmers choose.

In modern agricultural production, the increase in mechanization has shortened the growth period of hybrid rice, causing yield declines, increased seeding rates, and poor returns from rice farming.

How can competitiveness be improved?

Modern agriculture has placed higher demands on hybrid rice, but the urgent tasks are to lower hybrid rice seed prices, breed varieties with suitable growth periods, and greatly improve rice quality without affecting yield.

Lowering seed prices is the hard truth

“Farmers want less input and more output. No matter how you put it, in the end the seed price must be low.” Chen Liyun said, “At present, relying on scientific and technological progress to lower hybrid rice seed prices is effective.”

By breeding parents with ultrahigh outcrossing seed-setting rates, the seed production yield and commercial value of hybrid combinations can be greatly increased. The dual-purpose genic male sterile lines Chuang 5S (Qiong Shen Dao 2013020) and Yun 9S (Xiang Shen Dao 2012022) bred by Chen Liyun have particularly excellent agronomic traits, and their sink capacity has approached the level of the hybrid rice control in regional trials, giving them the potential for ultrahigh-yield seed production; their stigma exsertion rate is high, vitality is strong, and compatibility is good. When the flowering periods of the parents meet, the outcrossing seed-setting rate can reach more than 75%; flowering habits are little affected by abnormal weather, and under high or low temperature conditions there will not be a large number of closed glumes; they are not prone to sprouting on the panicle; the seeds do not crack or rarely crack, and the seed germination rate is high and stable. Compared with the dual-purpose genic male sterile lines currently used in large-scale production, seed production yield can be increased by more than 30%.