Inter-Specific Cotton Hybrids – How it All Began

31/12/2011 4:53:00 PM by Yechiel Tal, Ph.D.

Yechiel TalUpland cotton which belongs to the Gossypium hirsutum species of cotton constitutes most of the world’s cotton production and use (about 95%). Commercial varieties of this cotton are cultivated in all cotton growing countries. Many of the varieties are developed locally and so have been adapted to the particular local growing conditions. Some varieties of big international seed companies have a wide range of adaptation and are common in several countries.
Performance and yields depend on the variety and the growing conditions. In general, Upland cotton is regarded as having low to medium quality in fiber length, strength and fineness. However varieties differ according to their fiber characteristics; values range from less than 1″ to 1.17″ in length, from 24 to 29 gr’/tex’ in strength and fineness ranges from 3.5 micronaire (fine) to 6 mic’ (very coarse).

Textile mills use Upland cotton for most of their products but they like to use cotton of better quality to produce finer and stronger yarns for high quality garments.
For this purpose mills purchase lint of Extra Long Staple (ELS) cotton produced from varieties of Pima and Giza types which belong to another cotton species- G.barbadense.
This high quality cotton is characterized by very long fibers of 1.25″-1.45″ with improved strength of 33-42 gr’/tex and a good fineness usually of less than 4 mic.

World production of ELS cotton is very limited (about 5%) because it can only be grown in countries where growing conditions are favorable for these varieties.
They require a longer and warmer growing season than needed for Upland cotton with more water irrigation available. These conditions only prevail in a few specific regions of some cotton growing countries.

In addition, yields achieved from ELS varieties are usually 20-50% lower than those of the Upland variety grown under the same growing conditions. The limited and costly production of ELS cotton makes its price significantly higher than that of Upland lint.
Shortage of high quality cotton and its relatively expensive price also limits the use of this lint by the spinning mills. Hence, it is used mainly for mixtures with Upland cotton to improve the quality of yarn, with reduced costs.

The value of the variety’s output determines the grower’s income. High yield is the most important component to income generation. However, high lint quality contributes greatly to this income and may compensate for some yield loss.
Growers’ profits depend on the difference between gross income and cost production. Costs of production increase continually and growers look for ways to improve their income as well. When the yield potential is accomplished and there is no other way to save on expenses the only way to gain more profit is by improving quality.

So far there are no commercial varieties that combine the maximum yield potential of the best Upland varieties with the lint quality of the best Pima variety found in the crop.
This remains one of the most important challenges for cotton breeders.

Breeding for better quality

Improving the fiber characteristics of Upland cotton has been always one of the main, and common, objectives of breeding programs for cotton breeders. Any achievement in this respect will help with increasing the production and availability of better quality cotton for the textile industry everywhere.

In breeding new varieties cotton breeders tried to enrich their genetic germplasm from diverse sources. They usually conduct large cross programs between different genotypes and create highly segregated plant populations at several generations while selecting the best plants in each generation.
Finally, at the end of long process they hopefully select the individual plants with the desired traits. This is a common, conventional, breeding method known as Pedigree Selection.

In early breeding programs in the 1970s in California, USA some varieties of the Acala type were developed with better lint quality than most of the Upland known at that time.
In recent years new improved quality varieties were developed with fiber length up to 1.22″ and fiber strength up to 32 gr’/tex. These varieties are regarded sometimes as “Long staple” cotton. Still, this quality is not enough to meet the textile mills’ needs.

In the attempt to reach the goal of significantly improving Upland fiber characteristics, breeders also include in their programs crosses with plants of high quality belonging to the G.barbadense species.
The generations of these inter-specific crosses exhibit plant populations with a kind of variation that makes the selection of desired plants almost impossible.

Most of the plants obtained from these crosses were abnormal, sometimes sterile, and produced few bolls on big plants.
It was very difficult to select plants with acceptable performance out of these populations although some of them produced high quality fibers. Moreover, the breeder faced great difficulties in genetically stabilizing the selected plants which continued to segregate in the next generations.

This probably happens due to some genetic barriers between the two species related to the existence of linkage groups of genes in each of the species’ genome. Genes in these groups “prefer” to stick together and not to be mixed with foreign genes.
This phenomenon impedes the possibility of transferring desired individual genes that control fiber characteristics from Pima or Giza plants (G.barbadense) to Upland plants (G.hirsutum). Many attempts were made to break the linkage groups by repeated crossing but finally these crosses were found to be not successful.

Another breeding method for developing varieties is through hybridization of two breeding lines to form a hybrid variety of the first generation (F1). The two crossed plant lines become the parent lines of the hybrid variety.
Hybrid varieties are developed in many vegetable and field crops and most of them demonstrate clear advantages over regular conventional varieties.
Hybrid varieties of Upland cotton have been developed and grown successfully in India for many years. However, their fiber characteristic values are still typical to Upland cotton.
Hybrid varieties possess one set of genes from each parent line. So in fact, this method enables to also “mix” desired genes found in linkage groups in each of the parent lines even of different species.

Some research on Inter-specific (IS) crosses of cotton was carried out in the early 1970s by several breeders and researchers. Among them Prof. A. Marani in Israel and Prof. D. Davis in New Mexico studied the visibility and potential of IS hybrids.

They found the existence of new unique combinations of yield and fiber quality traits in these hybrids. They also observed strong Heterosis effects in IS hybrids compared to Heterosis that is usually found in Upland hybrids. These effects increase the expression of some traits over their expression in the crossed plants of the parent lines.
They point out that these hybrids may develop excessive vegetative growth that could affect the output negatively.

In the 1980s Prof. Davis conducted field tests with some IS hybrids to study and adjust the adequate management for their cultivation. Unfortunately, he had to stop his work when he couldn’t find an efficient and useful system for the seed production of these hybrids.
This happened despite the fact that at the same time another researcher, Prof. V. Mayer from Georgia, released breeding lines with germplasm that were supposed to facilitate the seed production. Davis started to utilize the new germplasm but couldn’t reach a desired, efficient production system.

It should be noted that hybrid seed production in India is still done by hand. Workers emasculate the female parent flowers and pollinate them with pollen from the male parent flowers. This process requires a lot of hand labor and can only be done where cheap hand labor is available in the required amount.

Personal point of view

In the late 1970s I began working as a plant breeder for the Hazera seed company in Israel. During my work I faced the difficulties of breeding new Upland varieties with improved quality or breeding Pima varieties with improved yield potential.
I learnt that the conventional breeding method is a long, frustrating, laborious process that usually resulted in very little progress.

At that time I already knew about the development of Upland hybrids in India. I also read about the research done on the IS crosses in the USA and Israel and was very impressed by the findings. So, I decided to study the possibility of adopting the hybrid approach in our breeding program in order to enhance the process and improve achievements.

In the early 1980s I started studying for my Ph.D. degree at the Hebrew University, as one of Prof. Marani’s students. In 1986 I submitted a thesis on “Dynamics of the development of yield components in Inter-specific cotton hybrids”.
While working on my thesis I became more confident that IS hybrids could be a real solution in overcoming the barriers in cotton breeding.
This belief led to Hazera starting a special breeding program for IS hybrids, including the introgression of the special germplasm needed for developing a desired seed production system.
In the late 1980s I met Prof. Davis in New Mexico and had the opportunity to observe his IS hybrids in the field and discuss various aspects of these hybrids with him.
I learnt more about the potential of these hybrids and about the obstacles he faced in cultivating them and producing their seeds.

Nevertheless, I was encouraged by what I saw and heard from Prof. Davis and tried to implement them in our program. I believed that it is worth taking risks and challenges to reach the desirable target in breeding IS hybrids to be significantly better varieties than conventional ones.

Activities and Achievements

Over years of comprehensive and intensive work in breeding IS hybrids we had to deeply study many important aspects that could affect the whole process up to the stage of commercialization. We’ve continually implemented what we learnt to improve our work in the following issues:

  1. Conducting a large program of test crosses to evaluate the combining ability of different breeding lines from both species. Hybrids obtained out of these crosses also helped us to learn about the heredity and expression of important traits when combined from these two species.
  2. Based on the above gained knowledge we developed criteria for selecting new pairs of breeding lines to be parent lines for the new improved IS hybrids. We had to ensure elimination of genotypes that may cause undesired heterotic effects in the performance of the hybrid such as excessive vegetative growth and poor fertility. Negative heterosis effects can also be seen in some fiber characteristics such as extreme fineness of around 3 mic or less.
  3. Preparing parent lines also included intro-gration (assimilating) of the germplasm necessary for efficient seed production. With this germplasm we’ve developed a genetic technology that enables us to produce hybrid seeds in an effective and economic system.
  4. All our female parent lines are full and stable male-sterile that save on hand emasculation. Some new female parents can be pollinated by insects and thus save on manual pollination. All male parents have the ability of full fertility restoration that ensures normal fertility of the hybrids under varied growing conditions.
  5. In order to make the most use of the hybrids’ potential we prepared a recommended protocol for cultivating the hybrids. It includes major guidelines for growers on how to adjust crop management to achieve better results.

The first line of Inter-specific hybrids was launched in the mid 1990s and all are characterized by their high lint yield with improved fiber quality, very similar to Pima’s.

They are adapted to grow under various growing conditions as the Upland cotton varieties are. Hence, they can significantly improve the cotton quality in many countries where Pima varieties cannot grow successfully. This possibility enables the grower to improve income and profit.

After a period of introduction and experimental cultivation in several countries the first hybrids were adopted for commercial cultivation in the USA (California), Peru, Spain, Ethiopia and Israel.

The most grown and most successful hybrid is called “Acalpi”, a name that expresses that its origin is from a cross between Acala and Pima genotypes.
So far, Hazera is the only company that offers seeds of commercial IS hybrids in the international market.

In conclusion, we can now say that much of the targeted challenge has been achieved. However, we continue to improve the hybrids’ output for the benefit of growers and new developed hybrids are being tested in more countries.
We have also up-graded the seed production system to ensure better availability of seeds.