Four groundnut (Arachis hypogaea L.) varieties (SAMNUT 21, SAMNUT 22, SMANUT 23 and SAMNUT 24) were grown in the Botanical garden, Department of Biological Sciences, Ahmadu Bello University, Zaria to determine the effects of defoliation on the growth and yield of the varieties. The experiments were laid out in a completely randomized design with five treatments (defoliation) levels. The plants were subjected to 5 levels of defoliation: 0 (no defoliation), 25, 50, 75 and 100% at 5 weeks after planting (WAP). The plants were sampled at 4, 7 and 10 WAP for assessment of growth parameters and at harvest the yield parameters were determined. The results of this study revealed that, 75% defoliation increased plant height in most cases. The control and 25% defoliation were found to increase root nodules, shoot and root dry matter, and shoot and root relative growth rate (RGR) in most cases. The 75 and 100% defoliation levels were found to significantly reduce vegetative parameters in groundnut varieties except plant height. The control and 50% defoliation had the highest flower production but flower production decreased with increase in defoliation with 100% defoliation level being the lowest in most cases. Total pods, number of matured pods per plant, haulms weight, pod dry weight and seed weight decreased with increase in defoliation but the number of immatured pods per plant increased with increase in defoliation level. The 25 and 50% defoliation levels were found to increase pod yield and haulms weight respectively but the
100% defoliation level produced the lowest yield in most cases. The data showed that varieties SAMNUT 22 and SAMNUT 21 showed higher values in vegetative parameters and yield parameters than the other varieties. Also, SAMNUT 23 showed the lowest values in both vegetative and yield parameters. In conclusion, the impact of defoliation on both vegetative and yield varies among varieties. The 25 and 50% defoliation increased vegetative and yield parameters in most cases but the 75 and 100% defoliation levels adversely reduced plant development and yield.
1.1 Origin and Classification of Groundnut
Groundnut (Arachis hypogea L.) belongs to Family: Fabaceae, Sub-Family: Papilionaceae, Genus: Arachis and Species: hypogaea. It originated from Latin America and was introduced into West Africa by Portuguese traders in the 16th century (Shankarappa et al., 2003; Olawale et al., 2014). The origin of this crop dates back to 350 BC (Hommones, 1994). Hommones, (1994) also reported that, the first probable domestication of groundnut took place in the valley of the Panama and Paraguay River System in the Grain Chaco area of South America and then move to the North America through slave trade.
1.2 Botanical Description
Reports showed that the cultivated groundnuts are divided into two large botanical groups:
„Virginia‟ and „Spanish-Valencia‟, on the basis of branching pattern “alternate” and “sequential”. They stated that these cultivars are group within the two branching pattern considered as subspecies. In the „Virginia‟ group, the main stem does not have reproductive axes. Alternating pairs of vegetative and reproductive axes are borne on the laterals branches and on other branches. In the „Spanish- Valencia‟ group, reproductive branches are borne in a series on successive nodes of the cotyledonary and other lateral branches, on which the first branch is always reproductive. Reproductive branches are also borne directly on the main axis at higher nodes (Prasad et al., 2010).
1.3 Requirements for Groundnut Growth
Groundnut is essentially a tropical plant and requires a long and warm growing season. The favourable climate for groundnut is a well-distributed rainfall of at least 500mm during the crop-growing season, and with abundance of sunshine and relatively warm temperature (Weiss, 2000). Weiss (2000) added that temperature in the range of 25 to 30oC is optimum for plant development and warm and moist conditions are very favourable than cool and wet climate, which results in slow germination and seedling emergence, increasing the risk of seed rot and seedling diseases. Msrivani (2009) reported that, temperature is the major environmental factor that determines the rate of crop development. Temperature above 350C inhibits the growth of groundnut, adequate and well distributed rainfall during the growing season especially during flowering, pegging and pod formation stages, is essential for maximum yield and quality of groundnut (Msrivani, 2009). Groundnut requires 500 to 1600mm of rainfall, which may last for 70 to 200 days of rainy season in the Sudan Savannah. It also requires well drained light coloured loosed friable sandy loamy soil, optimum moisture in pod zone and mean daily temperature of approximately 300C.
1.4 Areas of Growth and Production Level
Misari et al. (1980) reported that, agro ecological zone of groundnut production are the Sahel
(120 to 130N), Sudan (100 to 130N) and Northern half of the Guinea savannah (60 to 80N). Major groundnut zones are the Sudan and the Guinea Savanna where the soil and agro climatological conditions are favourable.
The production of groundnut varies from 3,500 kg/ha in the United States of America to 2,500 kg/ha in the South America, 1,600 kg/ha in Asia, and less than 800 kg/ha in Africa. This variation is due to mainly to various abiotic and biotic constraints (Prasad et al., 2010). In Nigeria, cultivated area under groundnut is about 1.0 to 2.5 million hectares annually and yields ranged of 500-3000 kg/ha. The seed yield in northern Nigeria is about 3000 kg/ha (Taru et al., 2008). In Nigeria, groundnut is produced in almost all the Northern States, the leading producing states include: Niger, Kano, Jigawa, Zamfara, Kebbi, Sokoto, Katsina, Kaduna, Adamawa, Yobe, Plateau, Bauchi, Borno, Taraba, Gombe and Nassarawa (Anonymous, 2010). Commercial production of groundnut in Nigeria is concentrated in the Northern parts of the country particularly in areas between the Northern Guinea and Sudan Savanna zone (NAERLS, 2006). However, due to the high commercial value and the attendant high demand, the crop is now gaining popularity as a cash crop for peasant farmers in the southern parts of Nigeria. But unlike in Northern Nigeria where recommendations have been made for plant densities and phosphorus fertilization for guaranteed stable yields of groundnut (NAERLS, 2006), such authentic and vital information are yet to be made available in the humid parts of Nigeria where the prospect for commercial cultivation of the crop is high.
1.5 Economic Importance and Uses of Groundnut
Groundnut (Arachis hypogaea L.) is an important oil seed crop as its seed contains 44-56 % oil and 22-30 % protein on a dry basis (Reddy et al., 2003). Groundnuts are used for oil extraction, food and as ingredient in confectionary products. Following the oil extraction, the residual cake is processed largely for animal feed, but it is also used for human consumption. Quality attribute that are important for end use of groundnut vary among the developed and developing countries. Groundnut also has a variety of industrial end uses, for instance; paint, varnish, lubricating oil, leather dressings, furniture polish, insecticides and nitroglycerin are made from groundnut oil. Soap is made from saponified oil and many cosmetics contain groundnut oil and its derivatives. The protein portion of the oil is used in manufacturing of some textile fibres.
Groundnut shells are used in the manufacture of plastic, wallboard, abrasives, fuel, cellulose (used in rayon and paper) and mucilage (glue) (Anonymous, 2011).
National Peanut Council (NPC) (2002) stated that, groundnut is used for making margarine, candy, salted groundnut, crackers/cookies, salad oils and soaps. It was however reported that, almost every part of the groundnut plant is used in some ways. According to Idama (2000), over 330 products can be commercially produced from groundnut and jobs can be directly created from massive groundnut production with small improvement in the technology and the use of improved variety with corresponding increase of cultivated hectares.
1.6 Problems of Groundnut Production
According to Akobundu et al. (1998), farmers are faced with erratic rainfall, decreasing soil fertility and inadequate supply of inputs. They added that some of the constraints that limit groundnut production include: soil degradation due to wind erosion, pest (i.e. nematodes and termites), decreasing yield, lack of availability of key inputs (seeds, fertilizer and agriculture equipment) and lack of food security. Akobundu et al. (1998) also stated that, the natural resources degradation, desertification, higher auto consumption levels and declining seed quality leading to lower yields. Ihejirika et al. (2008) carried out experiment with Groundnut variety P1274/191 to examine the effect of insects‟ defoliation and concluded that groundnut obtained highest damage from insect pests among other pests (Ihejirika et al., 2008). The foliage beetle Ootheca mutabilois produces characteristic inter-veinal holes in the leaves of the young plants (NRI, 1996; Ihejirika et al, 2008). Insect pests are an important factor in the infliction of injury on crops (crop damage) and also they act as vectors of plant pathogens, insect pests among others cause considerable loss to groundnut farmers in Nigeria (Ihejirika et al, 2008). Adult beetles and larvae feed on the pods and leaves of groundnut causing numerous small holes (NRI, 1996). Leaves injuries delay plant development, photosynthetic activities and reduce yield (NRI, 1996). Groundnut sucking bug, Rhyparochromus litotoralis (Dist.), is one of the most important insect pests of groundnut in Northern Nigeria (Samaila and Malgwi, 2012). They added that R. litotoralis commonly known as Lygaeid bug, or groundnut pod sucking bugs, which belong to the order Heteroptera and family Lygaeidae is found in all groundnut areas in India and in large clusters in the North eastern part of Nigeria, where it is known to cause serious damage to groundnut during harvest, but detailed record on history, biology and it‟s life cycle is lacking in Nigeria (Samaila and Malgwi, 2012). However, the closest member of the order Heteroptera to this bug based on close observation is the groundnut hopper (Hilda patruelis) (Heteroptera: Tettigometridae). Malgwi and Onu (2004) reported that, the detailed life history of this pest is not known, in spite of the fact that they are found in large numbers under harvested groundnuts in the field.
The production of this crop of great economic importance is facing decline in yield due to several factors of which leaves eating insects is one of the chief factor. Therefore, there is the need to evaluate the available groundnut varieties for their response to defoliation conditions.
1.7 Statement of Problem
Groundnut is one of the most popular commercial crops in Nigeria which account for 70% of the total Nigeria export earning between 1956 and 1967 but declined between 1957 and Mid1980s due to combined effect of drought and diseases (Taru et al. , 2008; Samaila and Malgwi 2012; Girei et al., 2013). Legumes are not properly protected from insects in tropical and subtropical countries, therefore, leaf eating insects and diseases are common in tropical and subtropical countries where farmers do not protect their crops adequately (Mondal et al., 2011). Adult beetles and larvae feed on the pods and leaves of legumes causing numerous small holes, this injuries delay plant development of photosynthetic activities and reduce yield (NRI, 1996). Due to high economic value of groundnut there is the need to determine the effect of defoliation levels on some of the available groundnut varieties in the guinea savanna zone of
Information about the reaction of these groundnut varieties to defoliation are not well documented in literature most especially in Nigeria. This research will provide information on the reaction of groundnut varieties to defoliation and thereby identify those resistant to
The aim of this study is to evaluate the effect of leaf defoliation on the growth and yield of groundnut varieties.
The objectives of this study were:
- To determine the effect of defoliation on the vegetative growth parameters of groundnut
- To determine the effect of defoliation on the yield parameters of groundnut varieties.
- Leaves defoliation does not have effect on the vegetative growth parameters of groundnut
- Leaves defoliation does not have effect on yield parameters of groundnut varieties.
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