Abstract: This study was conducted to evaluate the fresh pod yield, some plant and pod characteristics of eight local cowpea genotypes and two registered cowpea cultivars as control during 2001-2002 and 2002-2003 plant growth season in Samsun. Plant height, number of branches per plant, days to first pod setting, fresh pod harvest period, number of pods per plant, average pod weight, pod length, width, thickness, flesh thickness and seed coat, flower and pod colour were determined. Simple correlations were also calculated between fresh pod yield per plant and all investigated traits. The highest fresh pod yield per plant was in G10 genotype (110.23 g plant-1). This was followed by registered cowpea cv. Karagoz-86 (81.92 g plant-1), Akkiz-86 (58.12 g plant-1) and Kirazlik1 (54.55 g plant-1). Positive and highly significant (P<0.01) correlations were found between fresh pod yield per plant and fresh pod harvest period, number of pods per plant, average pod weight, length and width. There were also positive and significant (P<0.05) correlations among fresh pod yield per plant, number of branches per plant and pod thickness.
INTRODUCTION
Cowpea (Vigna unguiculata L. Walp.) is grown mainly in India and West Africa, but is also important in some areas of America and as green vegetable in the East Indies and China[1]. Cowpea, an annual legume, originated in Africa and is widely grown in Africa, Latin America, Southeast Asia and in the southern United States. Cowpea is a warm-season crop well adapted to many areas of the humid tropics and temperate zones. It tolerates heat and dry conditions, but is intolerant of frost[2]. Dry seeds and fresh pods of cowpea are used as human food and vegetative parts as feed for animals.
Dry cowpea sowing area and production of Turkey was 2900 ha and 2000 tons in 2001, respectively. Amount of cowpea production as a vegetable for fresh pods was 12000 tons for the same year. Cowpea is widely grown in Aegean and Mediterranean regions of Turkey. Leading vegetable cowpea producer provinces in Turkey are Izmir (3980 tons), Aydin (1967 tons), Manisa (1790 tons), Mugla (1242 tons), Hatay (1135 tons) and Balikesir (991 tons)[3]. In the middle Black Sea region, cowpea is cultivated in some provinces, districts and villages to supply only family requirements. These are Sinop, Kastamonu and some villages of Samsun’s Carsamba district[4].
There has been limited research on cowpea cultivation in Turkey[4-13]. Except for Peksen et al.[12], most of current research is related to cowpea growing for dry seeds. Currently, there are two registered cowpea cultivars, namely Akkiz-86 and Karagoz-86, in Turkey. These are mainly cultivated for their dry seeds as human food.
The study was conducted to compare two registered cowpea cultivars and eight local genotypes from different locations in Turkey, in terms of fresh pod yield, some plant traits and pod related characters. In addition, correlations among all investigated characteristics were examined.
MATERIALS AND METHODS
The study was carried out in the experimental area of Faculty of Agriculture, Ondokuz Mayis University in Samsun during 2002 and 2003 years. Two registered cowpea cultivars (Akkiz-86 and Karagoz-86) as control and eight genotypes from different locations in Turkey were used in the study (Table 1). Days to first pod setting from sowing and fresh pod harvest period as days between first and last pod harvest were recorded. Plant height, number of branches and pods per plant, average pod weight, pod length, pod width, pod thickness, pod flesh thickness and fresh pod yield per plant were determined in ten plants randomly selected from each plot.
| Table 1: | The names and collection sites of cowpea genotypes in the study |
| * Registered by Ege University, Faculty of Agriculture | |
A total of 100 pods randomly selected from those ten plants were measured in order to determine pod related characteristics. Fresh pod yield was obtained by harvesting pods at the green mature stage three times a week over a period of 8-11 weeks. Seed coat, flower and pod colours of genotypes were noted. The soil of experimental area was heavy clay, slightly acidic, without lime and salt, medium in phosphorus and rich in potassium and organic matter. Seeds were sown by hand 5 row plots of 3 m length, with 60 cm between the rows and 10 cm between plants. Sowing was performed on 23 May 2002 and 20 May 2003.
The experimental design was a randomized complete block (RCBD) with three replications. Combined analysis of variance over years was performed. MSTATC PROGRAM (Michigan State University) was used to carry out statistical analysis. Means showing significance statistically were compared using Least Significance Difference (LSD) Test at 0.05 or 0.01 probability level related to significance level of means. The correlations between fresh pod yield per plant and investigated characteristics were also examined.
RESULTS AND DISCUSSION
Seed coat, flower and pod colour and some pod characteristics were given Table 2. It was determined that flower colours of registered cowpea cultivars of Akkiz-86 and Karagoz-86 were white. Kirazlik1 had light purple flowers and the rest of the cowpea genotypes had purple flowers. Green pod colour for vegetable purpose are preferred by consumers. Pod colour was yellowish-green in G10, while it was green in all of the other genotypes. However, G10 and Karagoz-86 had also purple coloured section at the end of the their pods. Heavy pigmentation was the typical characteristic for Karagoz-86. Pod shapes and lengths of cowpea genotypes are shown in Fig. 1. Harvest time has a great effect on the occurrence of strings in fresh cowpea pods. Pods were stringless in all genotypes, but stringiness occurred in fresh pods for all of them with delay in harvest time.
| Table 2: | Seed coat and flower colour and some pod characteristics of cowpea genotypes |
| Fig. 1: | Pod shapes and lengths of cowpea genotypes used in the study. (1) G10, (2) Kirazlik1, (3) Kirazlik2, (4) G18, (5) Igdir, (6) Dalbahce, (7) Doganca, (8) Duragan, (9) Akkiz-86, (10) Karagoz-86 |
The analysis of variance showed that there was highly significant differences among all investigated plant and pod characteristics with the exception of pod flesh thickness (Table 3).
Plant height varied between 62.80 cm in Kirazlik2 and 120.90 cm in G10. These results are in close agreement with earlier reports of Gulumser et al.[4]. Plant height of G10, Doganca, Duragan and Karagoz-86 had highly significantly higher than the others.
The highest number of branches per plant was determined in G10 (1.80) and Karagoz-86 (1.57). The rest of the genotypes had significantly lower number of branches per plant and there was no significant difference among them (Table 3).
Genotypes used in the study showed highly significant differences in terms of days to first pod setting and pod harvest period. G18 (57.83 days) was the most earliest genotype for days to first pod setting, while Igdir (76.00 days), Duragan (74.67 days) and Doganca (73.33 days) were the most latest.
| Table 3: | Means for some phenological and morphological characteristics and fresh pod yield in cowpea genotypes |
| * and ** P<0.05 and P<0.01, respectively | |
| Table 4: | Simple linear correlations among fresh pod yield, some phenological and morphological characteristics |
| * and ** represent P<0.05 and P<0.01, respectively | |
Gulumser et al.[4] reported that days to first pod setting ranged from 69.33 and 76.00 days among seven cowpea landraces under Samsun ecological conditions. These findings of Gulumser et al.[4] support the results.
Pod harvest period was shortest in Duragan (59.00 days) and Doganca (60.50 days). The others were not statistically different from each other for pod harvest period. Pod harvest period shortened with delay in first pod setting (Table 3). Vural et al.[14] informed that the pod harvest period for cowpea is 5-9 weeks, depending on ecological conditions. Cowpea genotypes having a long fresh pod harvest period gave high pod numbers and fresh pod yield per plant, when compared with those having a short harvest period short.
The highest number of pods per plant was found in Karagoz-86, Akkiz-86 and Kirazlik1 and they were highly significantly higher than others. Although the lowest value for this variable was recorded in G10, the highest average pod weight (8.15 g), pod length (29.87 cm), pod width (5.83 mm) and pod thickness (6.92 mm) were also found in G10 genotype. Average pod weight was ranged from 2.06 g in Akkiz-86 and 8.15 g in G10. Mean values of cowpea genotypes varied between 10.90-29.87 cm for pod length (Fig. 1), 5.83-4.66 mm for pod width and 5.47-6.92 mm for pod thickness. There was no significant difference for pod flesh thickness among cowpea cultivars and genotypes used in this study (Table 3).
The highest fresh pod yield plant-1 (110.23 g plant-1) was recorded in G10 genotype. This was followed by Karagoz-86 (81.92 g plant-1), Akkiz-86 (58.12 g plant-1) and Kirazlik1 (54.55 g plant-1). The lowest fresh pod yield per plant was obtained from Kirazlik2 (35.18 g plant-1). It was not statistically different from Duragan, Doganca, Dalbahce, Igdir and G18 genotypes (40.09, 40.37, 41.85, 42.30 and 42.56 g plant-1, respectively) for this variable (Table 3).
Correlation analysis showed that fresh pod yield per plant was positively and highly significantly correlated with fresh pod harvest period, number of pods per plant, average pod weight, pod length and pod width. Positive and significant correlations were found between fresh pod yield per plant and number of branches per plant, pod thickness (Table 4). These results were in agreement with Jana et al.[15]. They found that pods number per plant had the highest direct effect on pod yield per plant. Kutty et al.[16] determined that number of pods per plant, number of picking, average pod weight and pod length had positively and significantly correlated with yield per plant. In order to select high yielding cowpea cultivars and to increase fresh pod yield, the pod harvest period, average pod weight and number of pods per plant should be taken into consideration. Similar results have been reported by Kutty et al.[16].
Tewari and Gautam[17] found that fresh pod yield was positively and significantly correlated with primary branches per plant, pods per cluster, clusters per plant, 100-seed weight and seeds per pod. In another study on pod yields and quality components, it was reported that pod length and fibre content were the major factors affecting pod yield in vegetable cowpea[18].
The number of branches per plant was positively and significantly correlated with average pod weight and pod length. These results were supported by Tewari and Gautam[17]. Fresh pod harvest period showed positive and highly significant correlation with number of pods per plant and fresh pod yield per plant (Table 4).
Negative and highly significant (P<0.01) correlation was found between plant height and pod harvest period, while plant height negatively and significantly correlated with pod number per plant. Correlations between plant height and average pod weight, pod length, pod width and pod thickness were positive and significant (P<0.05) (Table 4).
A preliminary study of consumer preferences for pod characteristics in vegetable cowpea showed a general preference for greener, longer, fleshier pods that are less seedy. Larger seeds, crowder pods and thin fibrous pod walls are characteristics of grain cowpea while they are often not preferred in vegetable cowpea[19].
In conclusion, G10 was the most favourable genotype due to its desirable pod characteristics for vegetable cowpea production. Although number of pods per plant was low in G10, the highest fresh pod yield per plant was obtained from G10. The greatest plant height, highest number of branches per plant, longest fresh pod harvest period, highest average pod weight, longest pods, widest pods and thickest pods were all obtained from G10. Karagoz-86, Akkiz-86 and Kirazlik1 were in same statistical group with G10 for fresh pod yield. G10 and Kirazlik1 can be recommended for fresh pod production as vegetable. However, Karagoz-86 and Akkiz-86 had some undesirable pod characteristics. Fresh pods of Karagoz-86 cultivar were restricted and it had larger seeds and crowder pods. In addition, there was a heavy purple pigmentation on pod surface of Karagoz-86, typical for it. Akkiz-86 had small pods ending conical section. Determined pod characteristics showed that Karagoz-86 and Akkiz-86 cowpea cultivars, registered mainly for dry seeds, were not suitable for use as vegetable cowpea.