3.3 Plants

Crosses between inbreds from different heterotic groups result in vigorous F1 hybrids with significantly more heterosis than F1 hybrids from inbreds within the same heterotic group or pattern (Figure 5). Heterotic groups are created by plant breeders to classify inbred lines, and can be progressively improved by reciprocal recurrent selection. [1]

Figure 5.Graph of heterosis features.

Heterosis is used to increase yields, uniformity, and vigor. Hybrid breeding methods are used in maize, sorghum, rice, sugar beet, onion, spinach, sunflowers, broccoli and cannabis.

3.3.1 Corn (maize)

Nearly all field corn (maize) grown in most developed nations exhibits heterosis. Modern corn hybrids substantially outyield conventional cultivars and respond better to fertilizer.

Corn heterosis was famously demonstrated in the early 20th century by George H. Shull and Edward M. East after hybrid corn was invented by Dr. William James Beal of Michigan State University based on work begun in 1879 at the urging of Charles Darwin. Dr. Beal's work led to the first published account of a field experiment demonstrating hybrid vigor in corn, by Eugene Davenport and Perry Holden, 1881. These various pioneers of botany and related fields showed that crosses of inbred lines made from a Southern dent and a Northern flint, respectively, showed substantial heterosis and outyielded conventional cultivars of that era. However, at that time such hybrids could not be economically made on a large scale for use by farmers. Donald F. Jones at the Connecticut Agricultural Experiment Station, New Haven invented the first practical method of producing a high-yielding hybrid maize in 1914-1917. Jones' method produced a double-cross hybrid, which requires two crossing steps working from four distinct original inbred lines. Later work by corn breeders produced inbred lines with sufficient vigor for practical production of a commercial hybrid in a single step, the single-cross hybrids. Single-cross hybrids are made from just two original parent inbreds. They are generally more vigorous and also more uniform than the earlier double-cross hybrids. The process of creating these hybrids often involves detasseling.

Temperate maize hybrids are derived from two main heterotic groups: Iowa Stiff Stalk Synthetic, often referred to as BSSS,[clarification needed] and non stiff stalk. [9]

3.3.2 Rice (Oryza sativa)

Rice production has seen enormous rise at least in China due to heavy uses of hybrid rice. (Figure 6)In China, efforts are being made to the fruitful extent by generating a super hybrid rice strain names as LYP9. It has the production capability in field condition to the extent of ~15 ton per hectare. In India also many varieties are released which has shown high vigor. Several promising varieties which were released include RH-10, Suruchi 5401 etc. [6]

Figure 6. Rise hybrid.

4. Practical application of heterosis

The phenomenon of heterosis has been observed in all the species studied. In many cases, heterosis is so obvious that there is no need to resort to statistical analysis to demonstrate its value. This is particularly true of corn hybrids. [6]