Introduction

Groundnut or peanut (Arachis hypogaea L.) is ranked as the world's sixth most important oil seed crop, contains 45~50% oil and 26~28% protein and is a rich source of dietary fiber, minerals and vitamins (Ntare et al., 2008). Groundnut is grown on 24.6 million ha worldwide with a total production of 41.3 million metric tons and an average productivity of 1.67 t/ha (FAOSTAT, 2014). Groundnut can be categorized in to two main groups according to the utilization pattern of the consumers. These are the oil types and confectionary types. Confectionary type groundnuts have some distinct characteristics, such as bigger seed size (>70 g/100 seeds), low oil content (30~35 per cent), rich in carbohydrates, high protein content with better blanching property (easy removal of the testa after roasting). Shape and size of pods as well as seeds are the important determinant factors of market price, particularly when the peanuts are used as food. Consequently, development of genotypes having high yield potential coupled with appropriate pod and kernel physical characteristics, which are the important attributes that always fetch premium price in the market, is the important objective in peanut breeding (Chuni et al., 2014). In Sri Lanka the majority of groundnuts are consumed as seeds without any value addition. Only a very few value added products can be seen in the market. Therefore it is very important to develop varieties which are suitable for preparing value added products and develop methods for value addition. In recent years Jumbo peanuts has become popular within the country. Still the total requirement for the jumbo peanut production is imported from other countries. As there is a demand for confectionary type groundnut at present, development of varieties to address the needs of local growers, manufactures and consumers is a timely requirement. Department of Agriculture, Sri Lanka has received confectionary type/large seeded groundnut accessions from various foreign sources. There is a need to evaluate the available large seeded groundnut genotypes to identify the extent of genetic variability within them and heritability of pod and kernel yield, for developing groundnut varieties. Therefore present study was carried out to identify the genetic variability of the large seeded groundnut genotypes available in Sri Lanka.

Results and Analysis

Growth and yield parameters were significantly different among lines indicated that there is a significant amount of variability among the genotypes. Significant (p=0.01) differences among groundnut genotypes for characters such as number of pods per plant, height of main stem, plant spread, days to 50% flowering, 100 seed weight and days to maturity (Table 1) were observed. The existence of higher magnitude of genetic variability for these traits has also been reported by Reddy (1995) suggesting ample scope for selection to improve these traits. Characteristics namely, Pod length and seed width were found to be significantly different among the accessions at p value of 0.05 level.

Number of days to flowering is one of the early indicators of the maturity of the genotype. The days to 50% flowering have been varied between 25 days to 35 days. ICGV 05200, ICGV 06189 and Satanoka were early flowering genotypes, while ICGV 05193, ICGV 05174, ICGV 06277, ICGV 06229, and Zambian variety along with two Japanese genotypes have taken long time for 50% flowering compared to other genotypes (Table 2).

All the genotypes tested were taken more than 100 days to mature. ICGV 05182, ICGV 06229, ICGV 05174 and ICGV 06211 genotypes were matured earlier than other types. Variety Walawa has taken 140days to maturity (Table 1). Majority of the genotypes have been mature around 120 days. Early maturing varieties are important as the most of the groundnut cultivation is done under rain fed conditions. Therefore 3 or 3.5 month age varieties are the most suitable for the cropping systems. The genotypes harvested within 4 months are needed to consider in the breeding program for further improvement. On the other hand longer aged varieties may be important if irrigated water is unlimited and the yield capacity of those lines is high.

Large variation was observed among the genotypes for pod weight per plant. This is may be due to the variation of the pod yield and the weight of the individual pod. Among the genotypes, ICGV 05200 has yielded the highest pod weight per plant. Significant amount of variability was shown for this character, while Variety Zambia recorded the lowest pod weight per plant (Table 1). 100 seed weight of the genotypes were varied from 40 g to 90 g. Both Japanese lines along with Zambia, ICGV 06229 and ICGV 05198 recorded a significantly high 100 seed weight comparing to others.

The pod yield per hectare in all the genotypes studied is shown in the figure 07. These yield were ranged from 1 500 to 4500 kg/ha. ICGV 05200 and ICGV 05198 has high pod yields of more than 4 000 kg/ha. The recommended variety Walawa has yielded around 3 000 kg/ha, while the yields of most of the other lines varied from 1 500 to 2 000 kg/ha. ICGV 05182, ICGV 06188 and two Japanese lines (Satanoka, Yatake) were low yielding genotypes according to the analysis (Table 2).

100 seed weight showed high heritability (84%) where genetic variance and the environmental variance were 139.7 and 25.1 respectively. Though number of pods per plant (57%) and pod weight per plant (67%) showed the heritability more than 50%, these characters are controlled by environment for a significant amount. Though 50% flowering is one of the parameters for early maturity, it is also controlled by the environment for a considerable degree. Days to maturity is highly heritable character (95%) according to the analysis (Table 3). According to Makinde (2013) very similar heritability estimates were recorded for days to maturity and days to 50% flowering. Previous studies indicated that high heritability is recorded for protein content, Seed size, pod yield per plant and 100 kernel weight (Parameshwarappa, 2005), suggesting that these traits are less influenced by the environment. This is essential for the traits to maintain the desirable confectionery standards when grown under varied environments.

Discussion

High level of genetic variability based on agro morphological characteristics was observed in the large seeded groundnut genotypes used in this study. According to qualitative characteristics, distinct variation can be observed among the genotypes. Plant height at maturity varied from 20 cm to more than 40 cm while plant spreading ranged from 50 cm to 85 cm, revealing that most of the genotypes showed spreading nature. Days to maturity was significantly varied among the genotypes, which most of the lines showed early maturity than the recommended variety Walawa. Number of pods per plant and pod weight per plant was significantly high in the genotypes namely ICGV 05200. 100 seed weight, which is one of the important trait in large seeded groundnut types, ranged  from 40 g to 90 g and Yatake, Zambia, ICGV 06229 and ICGV 05198 recorded high 100 seed weight. When considering the pod yield per hectare, it ranged from around 1 500 to 4 500 kg/ha, where ICGV 05200 and ICGV 05198 had high pod yields of more than 4 000 kg/ha. 100 seed weight and days to maturity were highly heritable characters while pod weight per plant and number of pods per plant were controlled by environmental factors for about 50%. It is evident that important traits such as 100 seed weight and day to maturity can be manipulated to a significant degree through conventional breeding procedures.

Materials and Methods

Nineteen large seeded groundnut lines used in this study were comprised of 15 lines received from International Crop Research Institute for the Semi-Arid Tropics (ICRISAT), one line from Zambia , two Japanese lines and check variety Walawa, which is the only recommended large seeded variety by the Department of Agriculture, Sri Lanka. The study was conducted at Grain Legumes and Oil Crops Research and Development Center, Angunakolapelessa, Sri Lanka during 2014/15 maha and 2015 yala seasons. The experiment was laid out in Randomized Complete Block Design (RCBD) with three replications. Plot size was 3 X 1.8 m and each plot was spaced one meter apart. Manually ridges were constructed within the each plot with the space of 45 cm. All DOA recommended cultural practices were followed and Supplementary irrigation was provided whenever necessary using flood irrigation. Agronomic and yield data were collected according to the groundnut descriptor published by Plant Genetic Resources Center, Department of Agriculture, 1995. The analysis of variance for different characters was done using SAS statistical software and the means were separated by Duncan’s method. Heritability (broad sense) was calculated according to the formula suggested by Hanson et al. (1956) for each character.

References

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