Designing African rainfed cotton ideotype by simulation

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Author

ROMAIN LOISON

CIRAD – France

Abstract

Crop simulation models (CSM) dynamically estimate agricultural production as a function of weather and soil conditions, and crop management. They can be used for evaluating cultivars in  actual and future tropical conditions. In Northern Cameroon, cotton (Gossypiumhirsutum L.) is grown exclusively in rainfed conditions and its yield has been decreasing steadily since the 80s. Therefore our objectives were to evaluate the usefulness of CSM to identify current rainfed cotton ideotypes for two contrasted environments of northern Cameroon. Based on field observations constituting the minimum dataset, phenology, morphology, leaf area index and  yield  simulated  by  CROPGRO-Cotton were successfully calibrated and validated in our conditions. Results showed that ideotype should have earlier anthesis date, longer reproductive duration, thicker leaves with higher potential assimilation rate compare to the reference cultivar (L484). In the North region, it seemed that having bigger leaf than L484 should be favorable whereas in the Far North  smaller ones are  more  suitable  to  local drought-prone conditions. We concluded that morpho-physiological traits could and should be imported into breeding programs in F5 generation where high genetic diversity still exist and plant material start to be considered as a line rather than a single plant. Consequently, we invite breeders to target cultivars with low “emergence to anthesis” to reproductive ratio, thick leaf, high chlorophyll content, and smaller leaf for the conditions with the lowest water availability and bigger ones for the conditions with best water availability.

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Morpho-physiological traits conferring drought adaptation among cotton genotypes in Cameroon

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Author

ROMAIN LOISON

CIRAD – France

Abstract

In Cameroon, water shortage is the major abiotic factor limiting cotton (Gossypiumhirsutum L) yield and lint quality. Understanding cotton physiological responses to water supply and their consequences on growth and development therefore provides insight into the problem of yield stagnation. The underlying strategies for yield maintenance under water deficit in Cameroon have not been well understood. The objective of this paper is to evaluate which ecophysiological traits could confer a good response to drought among a panel of cotton genotypes used in Cameroon. These genotypes were compared in field and  greenhouse trials under potential and water-limited conditions (fraction of soil transpirable water range: 0.39 to  0.83). Water deficit  had  a  negative impact on almost all the plant functions, both under field and controlled environments. The recent cultivar L484 bred for the driest production area responded quite differently from the other cultivars in this study. L484 had the fastest development, thickest leaves with the most chlorophyll and thus maintained the highest level of photosynthesis and transpiration per unit of leaf area in water-limited conditions. In these conditions, L484 had the highest radiation use efficiency and water use efficiency maintenances. However, despite the advances in cotton breeding in Cameroon, no significant improvement between old cultivars and recently released ones were found on biomass, harvest index and cotton yield across water conditions. The lint percentage was the only yield component significantly enhanced, irrespective of water status.

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Sixty Years Of Cotton Breeding In Cameroon: Interaction Between Genetic Improvement And Rainfed Cropping Conditions

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Author

ROMAIN LOISON

CIRAD – France

Abstract

Seed cotton (Gossypium  hirsutum L) yield in Northern Cameroon has been declining since the 80s despite breeding efforts. We used a set of widely grown cotton cultivars released at  different dates to study genetic improvement under different cropping conditions in Cameroon, and in controlled conditions. The genetic gain was estimated with a linear regression of the variety mean on its year of release (YR). Contrasts between genetic gains observed with different planting dates were estimated and tested. Our results revealed a genetic improvement on fiber yield of 3.3 kg ha-1 year-1 due to increased ginning out-turn. However, there was no genetic improvement on aerial biomass, harvest index or seed cotton yield. At the early stage of development, aerial and root biomass, and potential root extraction ratio of nutrients decreased with YR. So did leaf number and hairiness at the beginning of flowering. Carbon dioxide assimilation was not affected by YR. Neither were crop cycle duration and phyllochron. Although the potential of almost all fiber technological characteristics was improved under favorable water conditions, some (upper half mean length, short fiber index, uniformity index, and strength) were reduced in water-limited conditions. We concluded that cotton breeding efforts in Cameroon have successfully improved cotton fiber yield and the potential of most fiber technological characteristics. However, in water-limited conditions, fiber quality tended to decrease with the YR. There is still some room for seed cotton yield improvement.

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Ecophysiological analysis and modeling of genotype by environment by crop management interactions on cotton (gossypium hirsutum l.) in cameroon for the design of ideotypes

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Author

ROMAIN LOISON

CIRAD – France

Abstract

Cotton lint is the first natural fiber used in the world. Cotton provides income to more than 10 million people in West and Central Africa. In Cameroon, it is produced in rainfed conditions and water shortage is the major abiotic factor limiting yield and lint quality. In this context, a breeding program was initiated in 1950 to increase lint yield, fiber quality  and  disease resistance. After 60 years, this program has released more than 20 cultivars. However, seed cotton yield has been levelling off for more than thirty years. This study analyzed growth and development of main cultivars released from 1950 to-date to evaluate genetic gain including drought adaptation traits indirectly bred for. It also analyzed genotype by environment by crop management interactions (GEI) under water limited conditions in order to use a cotton simulation model in Cameroonian conditions. Then, crop simulation model was used to design cotton ideotypes under Cameroonian cropping conditions. An application of this work was in providing key drought adaptation traits to breed for cultivars that better withstand water stress. Firstly, phenotype evolution over breeding time and its interaction with cropping conditions in Cameroon was evaluated on cotton development, growth (including roots), yield, and fiber quality. Ten major cultivars were studied under rainfed conditions (field) and controlled conditions (greenhouse and phytotron). Classical GEI analysis of variance of cultivars and regression over their respective year of release were done. The results showed that the breeding program succeeded in improving cotton lint yield and the potential of fiber quality when the crop reached physiological maturity before the end of the rainy season. In  late  season drought, breeding reduced the fiber quality (fiber length, uniformity and strength). Most of the development and growth variables did not change with time, except the number  of leaves which  reduced.  Breeding  created cultivars with better potential fiber production and quality, but with reduced plasticity to sub-optimal environments and access to soil water. Secondly, an analysis of GEI for ecophysiological traits conferring a good response to drought was done in good and water limited conditions for a subset of four cultivars. The results indicated  that  water deficit  had  a  negative impact on almost all plant functions, both  under field and  controlled environments. The recent cultivar L484 bred for the driest production area had the fastest development, thickest leaves with most chlorophyll and thus maintained the highest level of photosynthesis and transpiration per unit of leaf area in water-limited conditions. In these conditions, L484 had the highest radiation use efficiency and water use efficiency maintenances. Despite these traits this cultivar did not show any improvement in terms of biomass, harvest index and cotton yield across water conditions. Cotton breeding program in Cameroon succeeded in providing a cultivar (L484) better adapted to local conditions, with a higher stability and faster development coupled with a strategy of growth maintenance, without any improvement in yield. Thirdly, the crop simulation model DSSAT CROPGRO-Cotton was used in order to design ideotypes with higher yield than existing cultivars. Field experiments in Cameroon were used to constitute the minimum dataset for the crop model calibration. Then, cultivars AC, L484 and forty-two virtual cultivars with ±20% from L484 parameter values were compared across 99 years of generated weather in two locations. Compared to L484, the cotton ideotypes in Cameroonian rainfed conditions had reduced emergence to anthesis duration, longer reproductive duration, higher level of photosynthesis maximum with thicker leaves, and smaller leaves for Far North region or bigger ones for North region.

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PROGRESS WITH VARIETAL IMPROVEMENT IN CIRAD

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CIRAD-CA (formerly IRCT), has participated in cotton research (mainly G. hirsutum) in a number of tropical countries in Africa, Latin America and Asia, for 45 years. Especially in cotton breeding, the work carried out has led to the creation of high quality plant material, well suited to the specific ecological conditions of the countries concerned and whose fiber qualities have progressively joined the best in their category. These varieties are grown currently on more than 1 500 000 hectares (ISA 205, STAM F, ISA 319, IRMA BLT, P 288, and glandless GL7). In the past, Ginning Out-Turn, a characteristic of great economical importance, has been improved. In fiber technology, the two main spinning processes (Open End and Ring spinning) have produced two types of demand, firstly for strong and fine fiber about 1″3/32 long (Open End) and secondly for high grade cotton with long and strong fiber (Combed ring spinning). In seed technology, the development of Glandless varieties can improve returns from  cotton growing. CIRAD CA participates actively in the training of national teams of breeders, provides assistance to the organisation of international research Networks (CORAF, Cono Sud) and makes efforts to master the new tools of biotechnology in view of giving access in the tropical countries to the benefits from progress made in genetic science. The introduction into cotton’s genomes of genes providing resistance to insects, opens up a new way of research, which could limit the use of insecticide sprays, with an economical and ecological impact on production costs and  protection of the environment.

Conclusion

CIRAD-CA varieties are grown each year on more than 1.5 million hectares in three continents, Africa, America and Asia. Modern CIRAD-CA varieties (GL7, ISA 205, ISA 319, P 288, STAM F, IRMA BLT) are well placed on the international market in relation to their competitors.

The glandless GL7 is currently the most widely grown variety in French-speaking Africa, with an extension of nearly 270 000 hectares. With this glandless variety, African growers have a plant that can be used simultaneously as a cash and a food-producing crop. The use of the glandless kernel requires encouragement, either in local villages, or industrially, to produce food for man or animals.

Ginning Outturn, Technology of fiber and glandless characteristic of the seed, have been the subject of a major research effort by the CIRAD-CA for the last ten years in Africa.  Much progress has been realised and fiber productivity /hectare increased 6 fold in 30 years in Africa.

The current evolution of the genetic programs at CIRAD-CA, concerns:

  • explicative research work aimed at a better understanding of the physiological adaptation of cotton plants to their environment.
  • developing particular efforts on the problems related to seed coat neps and stickiness.
  • engaging, over the last few years, in studies in biotechnology which are aimed at the genetic transformation of the cotton plant.

The role of the CIRAD-CA in co-operation assistance continues. Our knowledge of tropical countries and our experience with National Agronomic Research Structures, put us in a key position to help southern countries access the benefits of promising new technologies. CIRAD is a valuable partner for international cooperation.

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