GENETICS OF APHID (APHIS CRACCIVORA KOCH.) AND ROSETTE RESISTANCE IN GROUNDNUT (ARACHIS HYPOGAEA L.)
Groundnut production is largely constrained by biotic stresses with groundnut rosette virus disease seriously contributing to losses in yield in Nigeria and sub Saharan Africa and thus the need to study the mode of inheritance of aphid and rosette resistance in groundnut with these objectives; to investigate the gene action controlling the inheritance of aphid resistance, rosette resistance and other quantitative characters, to determine the relationship between aphid resistance, rosette resistance and other quantitative characters, to estimate the number of effective factors controlling the inheritance of aphid infestation, rosette disease and other quantitative characters and to determine genetic advance arising from selection against aphid resistance, rosette resistance and other quantitative characters. For this, two aphid resistance (ICGX-SM00020/5/9, P1 and ICGX-SM0020/5/P4/P1, P2), one rosette resistance, ICVIS07899 (P3) and one aphid susceptible, ICGX-SM0027/5/P10/P1 (P4), one rosette susceptible, Manipenta
(P5) lines were used as parents to develop F1s. The F1s were advanced to F2s and backcrosses made to the reciprocal recurrent parents. The seventeen generations obtained were evaluated along with three checks (Samnut 24, Samnut 25 and Samnut 26) in three replications using randomized complete block design at Institute of Agricultural Research Samaru, Zaria during 2014 growing season. Significant differences in mean performance among the parents and the F1s studied suggests sufficient variability across the generations for the characters studied. The three parameter model was adequate to explain variations observed in the inheritance of days to fifty percent flowering, plant height, number of seeds per plant and shelling percentage. It was inadequate to explain the variations observed in the inheritance of aphid infestation index, rosette disease incidence, rosette severity index, days to maturity, number of matured pods per plant, pod yield per plant and hundred seed weight hence, six parameter model was fitted. Non allelic
gene interactions were significant for number of matured pods per plant, pod yield per plant, rosette disease severity and rosette disease incidence. Dominance genes and epistasis bias the number of effective factors for days to fifty percent flowering, plant height, number of seeds per plant, shelling percentage, rosette disease incidence, rosette severity index, number of matured pods per plant and pod yield per plant hence, rendering the estimates less reliable. Wide ranges of narrow (33 to 95%) and broad (0 to 93%) sense heritability as well as genetic advance (0 to 32.3) were obtained for the characters studied. The genotypic correlation coefficients exceeded those of the corresponding phenotypic correlation coefficients for most of the character pairs indicating that the correlations were more genetic than environmental in the three sets of crosses. In conclusion, the set of groundnut crosses where non allelic interaction was significant with high narrow-sense heritability as obtained for rosette disease incidence, rosette severity index, number of matured pods per plant and pod yield per plant, it is possible to expect advance for these characters in further segregating generations. Broad sense and narrow sense heritability as well as genetic advance were moderate to high for most of the characters studied for the three sets of groundnut crosses. Genotypic coefficients of correlation were higher than phenotypic coefficients of correlation.
- 0 INTRODUCTION
Groundnut originated from South America in the coastal regions of Peru where evidence of its cultivation between 300 and 2500 BC is supported by archaeological reports (Stalker, 1997; Maiti, 2002). The crop is believed to have been distributed to other parts of the world by the Spanish and Portuguese explorers in the sixteenth and seventeenth centuries (Hammons, 1994). Groundnut (also known as peanut) belongs to the family Fabaceae, tribe Aeschymanomeneae and sub tribe Stylosanthineae. The genus and species names Arachis hypogaea were derived from Greek words arachos, meaning weed, and hypogea, meaning underground chamber (Holbrook and Stalker 2003). The species is classified into two subspecies: hypogaea and fastigiata based on the presence or absence of flowers on the main axis (Moretzsohn et al., 2004).
Groundnut is the fifth largest oil crop cultivated in more than 100 countries around the globe between lat 40o North and South of the equator (especially in Africa, Asia, North and South America ) (Waliyar et al., 2007). In 2015, groundnut was grown on a total area of 21.8 million hectare worldwide with an estimated production of 38.6 million tonnes (unshelled) at an average yield of 1.58 tonnes per hectare (FAO 2015). China, India, USA, Nigeria and Myanmar are the major producers of Groundnut. Developing countries in Asia, Africa and South America account for over 97% of the world groundnut area and 95% of total production. Nigeria and Senegal are the largest producers in West and Central Africa with 45% Africa total production (ICRISAT 2015). Groundnut is one of the most popular commercial crops in Nigeria. Nigeria produces 41% of the total production in West Africa (Echekwu and Emeka 2005).
Groundnut seeds contain 40-60 % oil, 20-40% protein and 10-20 % carbohydrate. The crop has high nutritional value, possessing vitamin E, niacin, calcium, phosphorus, magnesium, zinc, iron, riboflavin, thiamine and potassium. It is mainly used for direct consumption, in the confectionary industry, for vegetable oil in cooking and also as a source for protein feed in the animal industry. These multiple uses of peanut makes it an excellent cash crop for domestic as well as international trade (Manish et al., 2012). In West and Central Africa, it is an important food and cash crop: a major source of dietary oil and cash income for both urban and subsistence dwellers (Olorunju and Ntare 2001). As a legume, groundnuts improve soil fertility by fixing nitrogen and thereby increasing productivity of other crops in the semi-arid cereal cropping systems (Waliyar et al., 2007), and other ecological zones.
Groundnut production in Nigeria is constrained by several abiotic and biotic stresses among which is the groundnut rosette virus disease. Groundnut rosette virus disease (GRVD) has been recognized in all groundnut growing countries on the African continent, including its offshore islands such as Madagascar, but not anywhere outside Africa ( Nigam, 2008). GRVD is responsible for an annual groundnut loss of worth US$ 150 million (Waliyar et al.,2007). Nigeria alone lost about 0.7 million hectares of land to groundnut rosette virus epidemic which amounted to US$ 250million in 1975 (Yayock et al., 1976). The disease results from the synergistic interaction of three viral components; groundnut rosette virus (GRV), its satellite RNA (Sat-RNA), and groundnut rosette assistor virus (GRAV) (Taliansky et al., 2000). The disease is spread by groundnut aphid.
Groundnut aphids, Aphis craccivora Koch, (Hemiptera: Aphididae) are an important group of insects with worldwide distribution. They are herbivorous insects that can affect plants directly or indirectly by feeding on the plant‟s sap. Most aphid species comprise a set of closely related populations which may have diverged genetically so that they could be considered as host races, incipient or sibling species (or subspecies) (Blackman and Eastop 2007). Groundnut aphid is the major pest of groundnut causing yield losses by feeding on phloem sap and through transmission of virus diseases (Padgham et al., 1990).
Viruses are the most difficult of all groundnut pathogens to control because no chemical substances (viricides) are available yet for eradicating viruses from plants (Olorunju and Ntare 2001). Insecticides for controlling virus vectors (groundnut aphids) are expensive and hardly available to farmers. Their application also poses detrimental effect to human health and environment. Improved cultural practices are not effective because farmers are reluctant to accept and adopt those practices (Waliyar et al., 2007). Host-plant resistance to A. craccivora in groundnut is recognized as the most effective, economic and sustainable method of limiting both the spread of the aphid and rosette viruses (Feakin 1973; Padgham et al., 1990).
This research work focussed on the studies of inheritance of aphid resistance and rosette resistance in groundnut based on host-plant resistance mechanism with these objectives;
- To determine the gene action controlling the inheritance of aphid resistance, rosette resistance and other quantitative characters.
- To determine the relationship between aphid resistance, rosette resistance and other quantitative characters.
- To estimate the number of effective factors controlling the inheritance of aphid infestation, rosette disease and other quantitative characters.
- To determine genetic advance arising from selection against aphid, rosette and other quantitative characters.