Screening of Ricebean [Vigna umbellata (Thunb.) Ohwi and Ohashi] Cultivars against Pulse Beetle [Callosobruchus chinensis (L.)]

Pulses are important food crops that provide the nutritional requirements to human beings. Numerous pulse crops are grown in India under a variety of agro climatic conditions, of which the pulse crop, ricebean [Vigna umbellata (Thunb.) Ohwi and Ohashi] is an important food legume. Similar to other Vigna species, ricebean is a versatile crop that is mostly grown as a dry pulse and also used as green manure and fodder. It is an important pulse in Nagaland and is commonly referred to as ‘Naga Dal’. It is a traditional and native crop and there are many landraces of ricebean under cultivation in Nagaland (Shitiri et al., 2019). During 2020-21 the total production in Nagaland was 5,730 MT from an area of 4,970 ha (Anonymous, 2021).
       
Insect pests of both field and stored products are one of the major constraints limiting the production of pulses. Among the insect pests, Callosobruchus chinensis (L.) is the most important bruchid that causes considerable damage to Vigna seeds. It is estimated that infestation by C. chinenesis causes about 55 to 60% loss in seed weight and 45.50 to 66.30% loss in protein content (Kutbay et al., 2011). The damage due to this pest affects seed viability as well as the nutritive value of the seed. For the management of bruchids, conventional treatments methods have been used so far.
       
However, keeping the environmental aspects in mind, there is a need for ecologically sound methods like cultivating resistant varieties would be ideal and promising method too (Pradhan et al., 2020). The use of bruchid-resistant cultivars has considerable potential to minimize the loss in storage (Dongre et al., 1996). Various physical factors such as colour, shape, texture, size, etc. and bio-chemical composition such as protein, phenols, flavonoid, tannin, starch, fats, etc. influencing feeding and ovipositional responses have been studied by various workers and found that there is a substantial difference in host suitability and preference by bruchid on different varieties (Tripathi et al., 2015; Ghosh et al., 2022; Saravanan et al., 2023). Therefore, it is imminent to screen the cultivars and determine the factors influencing differential preference by the pest so that the information generated can be explored in resistance breeding. Keeping the above aspects in mind the present study was carried out to screen ricebean cultivars against pulse beetle, C. chinensis.

The experiment was conducted at the Department of Entomology, SAS, Nagaland University during January”June of 2019 and 2020. A total of 16 cultivars of ricebean collected from different parts of Nagaland were used for screening against pulse beetle, C. chinensis (Fig 1).
 

 
Screening of ricebean cultivars against C. chinensis
 
In order to screen the ricebean cultivar, ‘no choice test’ (Ponnusamy et al., 2014) was adopted by a Completely Randomized Design (CRD) with three replications. The experiment was conducted under controlled temperature of 28±2°C in BOD incubator. In a container with a perforated lid, 25 seeds of each cultivar were kept, four pairs of well-characterized, newly emerged male and female pulse beetle were released into the container and observations were recorded.
 
Oviposition and adult emergence
 
The pulse beetles were left in the containers for ten days for the purpose of oviposition. The number of eggs laid was recorded. Observations on adult emergence were recorded at a regular interval of 24 hours until no further emergence occurred for 5 consecutive days. The per cent adult emergence was calculated using the formula:
  Development period
 
The time taken from the release of the insects to the first adult emergence and the number of adults emerged was recorded. The average developmental period was calculated by using the formula:  
Where,
D-Day at which the adults started emerging.
A-Number of adults emerged on D^th day.
 
Growth index
 
The growth index of the insect was determined by using the formula:
   
Where,
S = Per cent adult emergence.
T = Average developmental period (days).
       
The cultivars were categorized based on the growth index as follows:
 


Per cent infestation and weight loss
 
From each cultivar 100g seeds were taken and four pairs of newly emerged male and female C. chinensis were released and were allowed for oviposition. The containers were left alone and adult emergence was observed i.e. for one generation.
       
The per cent infestation and weight loss of seeds was calculated using the formula below:
   
Evaluation of physico-chemical parameters of seed
 
The different physical characters and biochemical contents (Table 2 and 3) of the seeds were analysed. The seed index, size, coat thickness, shape, colour and texture of the seeds were recorded. The bio-chemical contents viz., protein, phenols, tannin, starch and fat contents were determined. The determination of phenol content was done by outsourcing at Indian Institute of Food Processing Technology (IIFPT), Thanjavur, Tamil Nadu. The protein content was estimated by Kjeldahl method (A.O.A.C. 1970), tannin content was estimated by Folin-Denis method (Schanderi, 1970), starch content was estimated by anthrone reagent method (Hodge and Hofreiter, 1962) and the fat content was estimated by using Soxhlet extraction method (A.O.A.C. 1970).
 
Statistical analysis
 
The data from different observations were transformed and subjected to Analysis of variance (ANOVA) and also by Duncan Multiple Range Test (DMRT). Correlation between different biological parameters of C. chinensis and physico-chemical parameters of ricebean cultivars were established.

Oviposition
 
The number of eggs laid ranged from 32.67 to 131.33 (Table 1). The cultivar Manyhü Rhi (32.67) was substantially less preferred for oviposition while Sipheghonu (131.33) was most preferred. The current study showed variation in oviposition preference on ricebean cultivars. Chakraborty et al., (2015) also reported variation in oviposition preference by C. chinensis on five pulses. The physical characteristics of the seeds as well as biochemical components may contribute to the oviposition preference of C. chinensis (Senthilraja and Patel, 2021; Paikaray et al., 2021).
 

 
Adult emergence
 
 The adult emergence was highest in the cultivar Sipheghonu (73.60%) and it was the least in cultivar Rhüjo (58.00%) (Table 1). The reduction in adult emergence could be due to non-preference of cultivar for oviposition. The results are in conformity with the findings of Arpitha and Sagar (2011).
 
Development period
 
The mean duration of development of C. chinensis ranged from 21.60 to 33.10 days (Table 1). The shortest development period was found in Kurhi Rhide cultivar (21.60 days). The maximum of 33.10 days was found in Mügo Rhi. The difference in the pest development period may be caused by certain physico-chemical characteristics of the seed. Chakraborty et al., (2015) and Bharathi et al., (2017) also reported similar findings in the developmental period of several pulses. The cultivars Sipheghonu and Kurhi Rhide, which were highly preferred for oviposition, showed a preference for development with less number of days. Similar finding was also reported by Khokhar and Singh (1987) in pigeonpea.
 
Growth index
 
Among the 16 cultivars, the growth index ranged from 0.057 to 0.086 (Table 1). Based on the susceptibility index the cultivars were grouped into 4 categories. The cultivars Rhüjo, Akixi Anila and Manyhü Rhi were moderately resistant; Pinchong Wethroi, Hera Ragei, Rhüluo, Ashei Nyakla, Hera Rahau, Kerhüand Rhüse were moderately susceptible; Kürhi Süre, Rhüdi and Khueishuei Shumei were susceptible and the highly susceptible cultivars were Sipheghonu, Mügo Rhi and Kurhi Rhide. Researchers frequently use the growth index to determine whether legume crops are resistant to bruchid infestation. In the present study none of the cultivars was found resistant to C. chinensis. The results are in tune with Tripathi et al., (2015) and Kavitha et al., (2018) who categorized pulses into resistant and susceptible varieties based on the growth index of pulse beetle.
 
Per cent infestation and weight loss
 
The per cent infestation by C. chinensis on different ricebean cultivars varied from 7.10 to 63.67 (Table 1). Among the cultivars, Sipheghonu had the highest percent infestation (63.67) and Rhüjo had the lowest percent infestation (7.10). The results are comparable with Khokhar and Singh (1987) who reported variation in per cent infestation by pulse beetle in pigeonpea varieties. The per cent weight loss varied from 3.73 to 11.07 (Table 1). The weight loss in cultivar Sipheghonu (11.07%) was highest. The minimum weight loss was observed in cultivar Rhüjo (3.73%). Similar findings were reported by Jatav et al., (2022) in green gram varieties. In the present study, cultivar Rhüjo had exhibited the lowest infestation and weight loss. In comparison to the other cultivars, the cultivar was less preferred for oviposition, adult emergence and delayed development period (days).
 
Physico-chemical parameters
 
The seed colour of ricebean cultivars varied from green to light green to yellowish-green, dark blue to creamy white, light yellow to light yellow with black spots and brown to light brown to light brown with black spots (Fig 1; Table 2). All the cultivars had smooth texture. The shape varied from nearly round to oblong. The seed coat thickness of the cultivars varied from 0.057±0.004mm (Hera Rahau) to 0.103±0.011mm (Pinchong wethroi). The seed size varied from 118.54±2.36mm² (Sipheghonu) to 19.46±0.71 mm² (Hera Rahau). The highest seed index was found in Sipheghonu (47.840.014g) and the least was in Rhüjo (5.280.008g).
 

       
The protein content among the cultivars ranged from 17.20 (Pinchong Wethroi) to 21.12 %. (Sipheghonu) (Table 3). The fat content of the cultivars varied from 0.51 (Kurhi Rhide) to 1.23% (Kurhi Süre). Phenol content showed significant variation among the cultivars. It varied from 80.06 (Sipheghonu) to 747.19 mgGAE/100g (Ashei Nyakla). Tannin content varied from 800.57 (Sipheghonu) to 1181.67 mgTAE/100g (Rhüjo). Starch content varied from 51.11 (Rhüjo) to 57.89% (Sipheghonu).
 

 
Correlation studies
 
The correlation studies (Table 4 and 5) showed that the biological parameters of the pest have a significant correlation with physico-chemical parameters of the ricebean cultivars. The present study revealed that the seed size and seed index have significant correlation with the biological parameters of pulse beetle (Table 4). The suitability of the pest increased by an increase in physical factors like seed size and seed index. The findings suggest that the larger the seed area, the greater the rate of oviposition, which results in more adult emergence leading to increased infestation and weight loss. The preference for larger seeds may be due to the availability of more space for oviposition, growth and development. Similar results were reported by Rathore and Chaturvedi (1997). In the present investigation, seed coat thickness did not show any significant correlation with biological parameters which is in conformity with Neog and Singh (2011).
 

 

       
The Biochemical content (Table 5) such as protein and starch showed a positive significant correlation with oviposition, adult emergence, growth index, per cent infestation and per cent weight loss and a negative significant correlation with the development period. The cultivars with higher protein and starch content were highly preferred by the pest for growth and development and were highly susceptible. However, phenol and tannin content showed a negative significant correlation. Cultivars having higher phenol and tannin content were less preferred by the pest and they exhibited resistance against C. chinensis. The findings are similar to that of Tripathi et al., (2013) who reported that the resistance observed in different cowpea accessions is due to biochemical factors such as protein and tannin. Kavitha et al., (2021) also reported a positive correlation of biological parameters with protein, sugar and moisture content and a negative correlation with phenol content.

In the present study out of the 16 ricebean cultivars screened against the pulse beetle C. chinensis, none of the cultivars was found resistant. However, cultivars viz., Rhüjo, Akixi Anila and Manyhü Rhi were found to be moderately resistant. These are potential bruchid-resistant cultivars and may be exploited in future ricebean improvement program. The physical characteristics viz., seed size and seed index and biochemical contents viz., protein, starch, phenol and tannin were found to be significantly influencing the host preference of the pest. Further investigations on biochemical content influencing the host preference can be undertaken in order to gain a better knowledge of the biochemical basis of resistance in various cultivars.

None.