INTROGRESSION OF STRIGA (Striga gesnerioides Willd) RESISTANCE INTO COWPEA (Vigna unguiculata L. Walp) VARIETIES

ABSTRACT
The parasitic weed, Striga gesnerioides (Willd) Vatke is one of the most important constraints to cowpea production in the dry savanna (Derived Savanna, Southern Guinea Savanna and Northern Guinea Savanna) of Northern Ghana. Yield losses due to S. gesnerioides range from 83 to 100%. No single method however, seems to be fully adequate in the control of this parasite. Host plant resistance, appears to have merit in effectively and economically controlling the parasite in that it is affordable to farmers. The objective of this study was to introgress Striga resistance into existing farmer-preferred cowpea varieties. Two resistant genotypes IT99K-573-1-1 and GH3684 were crossed to two susceptible varieties “Hewale” and “Asomdwee” respectively. The chi-square test was used to test the goodness-of-fit of the observed ratios to the expected genetic ratio in F2 segregating populations. The results of the cross of genetic of inheritance demonstrated 3R:1S ratio indicating single dominant gene action (monogenic inheritance). The result of the inheritance study indicated that the environment had great influence on a number of agronomic traits. The broad sense heritability for susceptible and resistant were high (63% and 78% respectively). Narrow sense heritability were low for some of the traits which is an indication that environmental factors (Striga) influenced cowpea production in this study. Three simple sequence repeat (SSR) markers SSR-1, C42-2B and 61RM2 associated with Striga resistance were used to screen 93 F2 progenies. The study showed that the three markers had discriminating power to distinguish between the resistant and susceptible genotypes and with presence of bands in resistant genotypes. The allele frequency for marker SSR-1 was 65% and 61RM2 was 73%, suggesting that these markers are highly repeatable within the population. Yield loss due to Striga infestation was estimated to be (78.22 to 87.17%). Other yield component including pods per plant, 100 seed weight, fodder yield, pod length as well as the number of seeds per pod of the susceptible genotypes were affected. There was significant correlation between percentage yield reduction and percentage reduction in various yield components indicating that Striga infestation was responsible for the overall yield reduction. At present very limited sources of Striga resistant varieties are available, therefore there is the need to develop new Striga resistant cowpea varieties that meet end-user preference. Promising lines will be screened with more Striga resistant markers to determine their level of genetic status.


CHAPTER ONE
1.0 INTRODUCTION
Cowpea (Vigna unguiculata (L.) Walp) is considered the most essential leguminous grain in the dry Savannas of tropical Africa. It is also known as the black- eyed pea or southern pea and is cultivated in a range of ecologies and cropping systems in the tropics. It originated from the semi-arid areas of West Africa and has been cultivated for human consumption for more than 4,000 years. (Tweneboah, 2000). The name cowpea probably originated from the fact that the plant was an important source of hay for cattle in the southern United States of America and in other parts of the world (Timko et al. 2007). Some important local names for cowpea include “Beng”in Dagari, “Ayi” in Ewe, and “caupi” in Brazil.

Cowpea is a member of the Phaseoleae tribe of the Leguminosae family (Timko et al 2007). It plays a critical role in the lives of millions of people in Africa and other parts of the developing world, where it is a major source of dietary protein that nutritionally complements staple low protein cereals and tuber crops. The high protein content present a major advantage in the use of cowpea as nutritional products, for infants and children and could compensate for the large proportion of carbohydrate often ingested in African diets (Lambot, 2002).

In Ghana, cowpea is an important source of vegetable protein and minerals for over 70% of the population and it is the second most important grain legume after groundnut in terms of production and utilisation (SRID-MOFA 2008). Notwithstanding its significance as human food, cowpea fodder is an imperative source of animal feed (Tarawali et al., 2002). Legume haulm provides an especially basic function in nourishing livestock during the harmmattan season in various West African countries (Tarawali et al., 1997, 2002, Tarawali 1997). Cowpea is a valuable and dependable commodity that generates income for farmers and helps to restore soil fertility for succeeding cereal crops growing in rotation with it.

Cowpea is an important crop in Ghana due to its contribution to national GDP, farmers incomes, food and nutrition security and sustainable agriculture (CORAF/WECARD Cowpea Report, 2011). The per capita consumption of cowpea in Ghana is about 9kg each year (Coulibaley et al., 2010). Ghana still import 3.380 metric tonnes of cowpea grains which augment the country production of 219,300 metric tonnes in 2010 (Egbadzor et al., 2013).

Regardless of the significance of black-eyed pea in West Africa, its production is still impeded by a myriad of abiotic factors. Biotic components, for example, pests and diseases, and parasitic weeds cause serious threat to cowpea production. The parasitic angiosperm Striga gesnerioides (Willd) is one of the significant limitations to cowpea cultivation particularly, in the Guinea Savanna agro-ecology. The parasitic weed S. gesnerioides is an obligate root-parasitic blossoming plant of the Scrophulariaceae family. Complete crop loss has been reported in susceptible cowpea genotypes following severe S. gesnerioides infestation (Muranaka et al., 2011). It is believed that the fast spread of this parasitic weed and huge yield decrease would constitute an extreme danger to cowpea production. For the resourced-poor farmers, developing S. gesnerioides-resistant cowpea genotypes in blend with fitting management practices are most conservative and effective choices to forestall yield loss brought on by this parasite which seeds are found in plenitude in plagued fields. The utilization of Striga - resistant cultivars lessens the parasite's seed multiplication and this exhausts the Striga seed bank (Badu-Apraku and Lum, 2007; Haussmann et al., 2004).

Over the years, the CSIR-Crops Research Institute has released cowpea varieties which are being grown all over the country. Examples of such varieties “Asomdwee” and “Hewale”. These varieties are known to be early maturing, high yielding and farmer preferred. They are also known to be adapted to Forest transition, Coastal and Savanna agro-ecologies but are susceptible to S. gesnerioides. These varieties are tolerant to other biotic and abiotic stresses and have consumer acceptability. However, the cultivation of these two varieties is a problem in the Savanna areas where S. gesnerioides is prevalent. The Savanna zones including Derived Savanna, Southern Guinea Savanna and Northern Guinea Savanna of Northern Ghana, constitute about 41% of Ghana’s landmass and major cowpea growing areas. Therefore, there is the need to address this Striga problem by developing resistant or tolerant varieties. This study sought to transfer Striga resistance into the background of two existing farmer-preferred cowpea varieties (“Asomdwe” and “Hewale”) using conventional and molecular breeding tools.

The main objective of the study was to introgress Striga resistance into two improved cowpea varieties using molecular breeding tools.

Specific objectives were to:

determine gene action controlling Striga gesnerioides resistance,

identify F2 progenies that may be resistant to S. gesnerioides using SSR and SCAR markers associated with S. gesnerioides resistance,

confirm Striga resistance in selected lines through inoculation in pot experiments, and

determine the yield loss due to S. geesnerioides in cowpea.

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Item Type: Ghanaian Postgraduate Material  |  Attribute: 103 pages  |  Chapters: 1-5
Format: MS Word  |  Price: GH50  |  Delivery: Within 30Mins.
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