Present Status And Future Prospects For Heterosis Breeding Biology

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The helianthus (Helianthus annuus L., 2n = 34) belongs to the family Compositae. It was given its name, “sunflower” (Gr-helios = Sun, anthos = flower), in Europe in the eighteenth century. Sunflower is one of the chief crops around the world, cultivated on a surface area of about 21 million hectares (Akcora et al., 2007).

It is one of three crop species, along with soybean and rapeseed, which accounts for about 78% of the world’s vegetable oil. Heterosis of these crops has been exploited only over the past few decades. Hybrid helianthus became a reality with the discovery of cytoplasmic male asepsis and an effective male fertility restoration system during 1970. Sunflower intercross breeding was started economically in detecting CMS by Leclercq in 1960 and restorer genes by Kinman in 1970 (Miller and Fick, 1997).

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The first sunflower hybrids were produced in the US in 1972 and reached 80% of production in five years (Fick and Miller, 1997). Single-cross hybrids rapidly became dominant in sunflower cultivars worldwide. Hybrids were preferred by farmers due to their high output and quality potential, homogeneity, simultaneous maturity, and easy possibility of cultural applications worldwide. Hybrid vigor has been the main driving force for acceptance of this oilseed crop.

Use of hybrid vigor has allowed sunflower to become one of the major oil-rich seeds in many states of Eastern and Western Europe, Russia, and South America, and it is an important crop in the USA, Australia, South Africa, China, India, and Turkey. Of the about 16.5 million hectares of sunflower grown in the major producing states, 11.5 million hectares are planted to hybrids (Miller, 1998).

Present-day sunflower cultivars contain more than 40% oil and 18-20% protein. Sunflower oil is of good quality as it contains a high proportion of linoleic acid, which is a polyunsaturated fatty acid. It is also a good source of calcium, phosphorus, niacin, and vitamin E. There are a number of advantages of growing helianthus for oil compared with other cultivated species. No special machinery is needed to produce this crop. It can be grown as a catch crop in many situations.

Being drought-resistant, it is well suited for rainfed as well as irrigated areas. Sunflower seeds contain about 42 percent high-quality edible oil. The crop duration is such that it can be sandwiched between two cotton, rice, or potato crops. So it has great potential to make the country self-sufficient in edible oil. It is necessary to improve the yield potential of sunflower varieties/hybrids to increase sunflower production in the country.

Hybrids, due to their higher yield potential, are being used throughout the world for increasing the productivity of almost all crops, including helianthus. With an area of 2.1 million hectares and production of 1.25 million tons, sunflower is one of the most important oil-rich seed crops in India. India’s share in the total world production of helianthus is about 6%, accounting for 10.0% of the world’s land area.

Sunflower is grown year-round as a sole crop, and it also fits well as an intercrop with legumes, in double cropping, and in three-crop rotations. Despite the prime position the crop holds in the vegetable oil economy of the country, the average productivity level is low (629 kg/ha) compared with the world’s productivity (1240 kg/hour angle ) . After the debut of the harvest in India in the early 1970s, a demand for loanblends was recognized. Experimental loanblends were developed in 1974-75 utilizing the centimeter and refinisher lines introduced from USA.

The first intercross from the public sector was released for commercial cultivation in 1980. Since then, the intercrossed breeding plan has been quite successful, and 29 productive loanblends have been developed by both public (18) and private sectors (11). These loanblends are intended for different agroproduction situations, which occupy 95% of the crop-grown area. According to the website of the board of directors of oil-rich seeds research in Hyderabad, India, eleven open-pollinated and 16 loanblends have been released under AICORPO.

Despite these successes with the crop, the major problems endangering sunflower productivity in India are the stagnating and unstable yields and exposure to various biotic stresses. The major diseases assailing helianthus crops in India are Alternaria leaf spot (Alternaria helianthi), rust (Puccinia helianthi Schw.), downy mildew (Plasmopara halstedii (Farl.), Rhizopus head rot, and a sunflower mortification disease (a disease of recent origin). The crop is affected at all growing stages.

Disease incidence is highly unpredictable and tends to fluctuate from year to year, season to season, and location to location, requiring region-specific management strategies. Among the various approaches to manage these diseases, host plant resistance is the most dependable and economical for the end-users. Plant breeding efforts to develop varieties/hybrids with built-in tolerance to the major diseases are constrained by the narrow genetic base of the cultivated helianthus. Development of loanblends from Inbred Lines

Loanblends are also developed from inbreds derived from the same narrow gene pool. A gene bank with about 1000 accessions is available in the state, but it is characterized by unacceptable levels of intra-accessional heterogeneity in many lines, thus restricting the scope for use of the material in breeding programs.

Most studies on breeding for disease resistance were confined to screening of the available cultivar germplasm against the diseases under natural conditions, and hence, these sources could not be converted into usable forms. With the exception of downy mildew disease, the released cultivars rated as tolerant/resistant are based on their field reaction to the pathogen. However, none of these were bred from parents that were classified as genetically immune to a particular disease.

Wild Helianthus species serve as potential sources of fresh genetic variability, and several desirable features such as resistance to biotic and abiotic stresses, cytoplasmic male sterility, fertility restorer genes, and oil quality have been successfully introgressed into cultivated helianthus (Seiler, 1992).

The growing demand for additional genetic variability to improve cultivated helianthus makes it necessary to collect, maintain, characterize, evaluate and utilize the wild helianthus germplasm. Concerted efforts are required to incorporate additional genetic variability from dependable sources by integrating modern biotechnological tools and conventional breeding methods. (Sujatha, 2006). Recently, a study of genetic diversity among 177 public helianthus inbred lines was carried out.

These inbred lines were developed and released by USDA-ARS from 1970-2005. Target region amplified polymorphism (TRAP) marker technique was found suitable for fingerprinting of helianthus inbred lines. These inbred lines will be useful for further hybrid breeding programs in helianthus (Yue et al., 2009).

Hybrid Choice

The choice of adaptable hybrids combined with the use of recommended production patterns is an important factor for profitable sunflower production. Hybrids are now planted on over 99 percent of the US land area. Hybrids replaced open-pollinated varieties because of their increased yield, pest resistance, uniformity, stalk quality, and self-compatibility.

Agriculturists should use several criteria in hybrid selection. First, they should take an inventory of available hybrids being marketed in their area. Seed yield potential is an important trait to consider when looking at an available hybrid list. Yield test results from university experiment stations and from commercial companies should identify a dozen or so consistently high yielding hybrids for a particular area.

Results from strip trials or demonstration plots on or near agriculturists’ farms should also be evaluated. Yield results from previous years on an individual’s farm and information from neighbors are also valuable. The best producing hybrids in a region may produce about 2,000 pounds per acre with good soil fertility and favorable soil moisture, or up to 3,000 pounds per acre in the most favorable growing conditions. North Dakota’s average yield ranges from 1,200 to 1,400 pounds per acre.

An important trait to consider is pest resistance or tolerance. Hybrids are available with tolerance to rust, Verticillium wilt, certain races of downy mildew, and early maturity. Agriculturists should check with their local seed dealer or sunflower seed company representative to obtain this information.

Stalk quality, another trait to consider, is the stalk’s reaction to damage from several pests. Hybrids with good stalk quality are easier to harvest, and field losses are generally reduced. Good stalk quality in sunflowers also allows the crop to withstand damage and field losses due to high winds. Uniform stalk height at maturity is another important trait to consider.

Oil percentage should be a trait to consider in hybrid selection. Several environmental factors influence oil percentage, but the hybrid’s genetic potential for oil percentage is also important. If the market price is influenced by oil percentage, then high oil hybrids should be considered. Current hybrids have oil percentages ranging from 38 to over 50 percent. Domestic sun oil crushers have been paying a premium for higher oil-rich seed in recent years. Hybrids with oil percentages in the 40-45 range, on a 10 percent moisture basis, should be selected.

Agriculturists should examine physiological maturity ratings to take advantage of sunflower hybrids, especially when considering late plantings. Agriculturists need a hybrid that will mature well within the average frost-free period. Compared to the mid-late 1970s, the maturity ratings of sunflower hybrids available today are much broader in scope of maturity (earliest to full season).

Test weight is also an important trait for consideration, particularly for hybrids selected for late planting or replanting. A test weight of 25 pounds per bushel is required to make official USDA grade, but recently developed hybrids have test weights ranging from 28 to 32 pounds per bushel.

Self-compatibility, the ability of the sunflower plant to pollinate itself in the absence of insect pollinators, is another desirable trait in hybrids.

Finally, the last point to consider is the purchase of the seed from a reputable seed company and dealer with a good technical service record if production problems do occur and assistance or consultation is required.

Cytoplasmic male asepsis for developing Sunflower loan blends

The discovery of cytoplasmic male sterility (CMS) in Helianthus by Leclereq (1969) and subsequent identification of genes for fertility restoration have resulted in the development of commercial hybrids since 1972. However, all commercially grown Helianthus hybrids have a single source of CMS discovered by Leclereq leading to homogeneity and potential risk, as seen in the case of corn. Diversification of CMS sources is essential in any hybrid-breeding program.

Fortunately, in sunflower, more than 62 new CMS sources of different origins have been reported (Serieys, 1999). The diversity of the new sources was evaluated primarily based on cytoplasmic male sterility and fertility restoration systems. Only a few researchers have described interactions between cytoplasms and nuclear genes in the expression of several qualitative and quantitative traits, and good cytoplasmic-nuclear interactions have been reported in various crops.

In Helianthus, a unique cytoplasmic-nuclear interaction caused a reduction in chlorophyll, photosynthetic rate, and overall energy and a positive effect on oil content. At present, the main objective of sunflower breeding is to obtain high-yielding commercial hybrids. Sunflower hybrids are the focus of breeding attention because of their agronomic and economic advantages over varieties (high productivity, oil content, disease resistance, etc.).

The key component of sunflower hybrid development is CMS. The obtaining of hybrids with high hybrid vigor effect became possible after the discovery of the first CMS source by P. Leclercq (Leclercq, 1969) and detection of fertility restoration genes by M. Kinman (Kinman, 1970).

Development of sterile CMS parallels of lines used in sunflower breeding programs for commercial hybrid development is one of the practical applications of CMS research. CMS PET-1 is a CMS source that is widely used in sunflower hybrid development. Such cytoplasmic uniformity presents a potential risk for hybrid sunflower production. The use of different cytoplasmic backgrounds in hybrid development will improve general variability of the Helianthus and reduce the risk of epidemics.

The different CMS lines and genetic stocks registered are presented in Table 1. Thirteen new sterile CMS parallels based on different Helianthus CMS sources have been obtained. The obtained backcrosses have been evaluated for main agronomic traits, including the resistance to the important Helianthus pathogens. As a result of this study, the most promising CMS parallels were designated for future use in breeding programs (Tavoljanskiy et al., 2004).

Cytoplasmic male sterility (CMS) in commercial Helianthus hybrids is thought to be derived from a related wild species, Helianthus petiolaris, yet CMS lines are known to carry the chloroplast DNA genotype of H. annuus. Commercial Helianthus hybrids released from Argentina are listed in Table 3.

To clarify the origin of sunflower CMS, a polymerase chain reaction-based scheme was developed for detecting CMS in Helianthus and surveyed more than 1,200 plants representing 55 accessions of H. annuus and 26 accessions of H. petiolaris. 160 offspring from three crosses were tested for strict maternal inheritance of organelle DNAs to determine if the apparent discrepancy in the species donor of the mitochondrial DNA and chloroplast DNA genotypes in CMS lines might result from low-frequency maternal or biparental inheritance of either organelle.

No CMS cytotypes were observed in natural populations of either H. annuus or H. petiolaris, and strict maternal inheritance of organelle DNA was observed. Pollen scarcity has been studied in an Indian hybrid KBSH-1 or when there is extra handiness of pollen from restorer line-6D-1 due to miss of synchronism and to hold better public-service corporation of available pollen.

Pollen grains may be stored either in icebox or in earthen pots filled with H2O and covered with wet fabric and utilised decently when male unfertile line-CMS234A is receptive, to acquire increased output ( Sumathi et al. , 2007 ) . The sunflower loanblends for downey mold opposition released by ICAR India are listed in table 2. Private sector seed companies have besides released many of import loanblends for cultivation, some recent 1s are listed in table 4.

Future changes

Contrary to conventional genteelness methods, the F1 intercrossed method facilitates the familial variegation of helianthus genotypes through a more efficient geographic expedition of the Helianthus genus with its possible cistron pools for superior quantitative and qualitative traits. The familial advancement already achieved will be further increased by modern methods of biotechnology and familial technology which will let development of a new ace productive type of helianthus.

The output advantage of FI loanblends compared with best open-pollinated assortments stands demonstrated. Unfortunately all soon available F1 loanblends are based on the petiolaris CMS beginning. More attempts must be directed towards variegation of exploitable CMS beginnings. With the rapid gait that characterizes the development of the modern molecular genetic sciences, the sunflower intercrossed genteelness can non come on correspondingly without the joint attempts of scientists and research institutes involved.

Constitution of an FAO research web on helianthus was a measure in the right way The chief current jobs of sunflower loanblend genteelness are the farther betterment of productiveness by increasing seed and oil outputs and the decrease of familial exposure to diseases and heat or H2O emphasis encountered in assorted ecological zones. ( Vranceanu 1998 ) .

New beginnings of CMS and birthrate Restoration cistrons will assist cut down the familial exposure of commercial helianthus loanblends because of the current usage of individual centimeter cytol, PET1 ( French ) derived from H petiolaris Nutt and a few birthrate Restoration cistrons These new centimeters and matching birthrate Restoration lines will supply cytoplasmatic diverseness for intercrossed sunflower production ( Jan and Vick 2006).

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