Based on per cent bruchid infestation the F
7 segregants were classified as highly resistant, moderately resistant, least susceptible, moderately susceptible and highly susceptible, as presented in the Table 2. As shown in Table 2, the per cent bruchid infestation varied much among the different classes, the highly resistant (HR) class recorded 16.09 per cent bruchid infestation and moderately resistant (MR), least susceptible (LS), moderately susceptible (MS), highly susceptible (HS) classes recorded 29.75 per cent, 48.49 per cent, 69.59 per cent and 83.06 per cent bruchid infestation respectively. Accordingly, top 15 resistant F
7 segregants are given in the Table 3. The results revealed that, F
7: 78-1-1 segregant recorded least per cent bruchid infestation (12.24%). Among the rice bean resistant germplasm lines RBHP-38 and IC18563 recorded zero per cent infestation, the variety DC 15 exhibited infestation of 26.53 per cent and considered as moderately resistant and DCS 47-1 reported 68.98 per cent infestation, regarded as moderately susceptible.
The results pertaining to number of adults emerged out of different classes of stabilized F
7 lines are depicted in Table 2. High degree of variation was observed among the different stabilized F7 lines. The highly resistant (HR) class reported 13.43 number of bruchids emerged, while moderately resistant (MR), least susceptible (LS), moderately susceptible (MS) and highly susceptible (HS) classes reported 32.21, 47.38, 52.83 and 56.25 number of bruchids emerged respectively. Considerably least number of bruchids were emerged in F
7 lines namely, F
7:78-1-1 (Table 3). As far as checks are concerned, checks RBHP-38 and IC18563 had zero number of bruchids emergence whereas, DC 15 and DCS 471 showed 21.0 and 34.0 adults respectively. The reason for resistance may be due to oviposition and antibiosis to egg and larva. Adult recovery is hampered by unpalatable physicochemical characteristics of grains.
The seed moisture content of different classes of F
7 progenies are presented in Table 4. The highly resistant (HR) class reported 7.57 per cent moisture content. While, moderately resistant (MR), least susceptible (LS), moderately susceptible (MS) and highly susceptible (HS) classes reported 8.09, 8.20, 8.81 and 9.09 per cent moisture content respectively, indicates the presence of considerable variability among different classes for seed moisture content. Similarly, seed moisture (%) of top 15 resistant F
7 progenies is presented in Table 5. The progeny, F
7: 78-1-1 contained minimum moisture (6.49%) followed by F
7: 59-3-1 (6.70%). Since there is difference among different classes, this clearly indicates that seed moisture content of genotypes influence the resistance or susceptibility against bruchids attack. While, the moderately resistant check DC 15 (MR) recorded 8.25 per cent moisture, moderately susceptible check DCS 47-1 (MS) recorded 9.10 per cent moisture. Highly resistant rice bean checks RBHP-38 and IC18563 have 8.01 and 8.06 per cent moisture respectively, So less moisture is associated with the resistant nature of the cowpea seeds.
In Table 4, results indicates the apparent weight loss (%) of different classes of F
7 families due to infestation of bruchids was minimum in the highly resistant (HR) class with 3.75 per cent apparent weight loss, while moderately resistant (MR), least susceptible (LS), moderately susceptible (MS) and highly susceptible (HS) classes reported 6.41, 8.87, 9.07 and 10.65 per cent apparent weight loss respectively. Among top 15 resistant lines mentioned in Table 5, the segregant F
7: 78-1-1 have less apparent weight loss with 2.48 per cent where it has values 6.36 and 8.24, in moderately resistant and susceptible checks such as DC15, DC S47-1 and 1.48 and 3.24 percent in resistant checks of ricebean namely RBHP-38 and IC18563 respectively. These results are in agreement with findings of
Divya et al., (2012) who stated that entries which were least favoured by bruchids for oviposition, adult emergence and insect recorded less percent weight loss are resistant to bruchids.
The results pertaining to the per cent actual weight loss in different groups of F
7 lines after infestation are presented in Table 5. There was a variability existed among the different F
7 lines. The highly resistant (HR) group showed 2.63 per cent actual weight loss, while moderately resistant (MR), least susceptible (LS), moderately susceptible (MS) and highly susceptible (HS) groups showed 5.29, 7.75, 7.95 and 9.53 per cent actual weight loss respectively. The actual weight loss (%) of top 15 resistant lines is given in Table 5. The results showed that the progeny F
7: 78-1-1 recorded least actual weight loss of 1.36 per cent respectively. Among the checks RBHP-38 exhibited minimum weight loss (1.10%), while IC-18563, DCS 47-1 and DC 15 exhibited 2.89 per cent, 6.34 per cent and 4.92 per cent actual weight loss respectively. The minimum actual weight loss is attributed to minimum adult emergence and less seed damage.
The seed germination (%) at initial and 45 days after release of bruchids was recorded (Table 10). The results show that the minimum reduction in germination percentage was seen in highly resistant class with 4.71% and it was followed by moderately resistant (MR), least susceptible (LS), moderately susceptible (MS) and highly susceptible (HS) classes reported 20.35, 38.71, 59.92 and 71.63 per cent reduction respectively. While among top 15 resistant lines (Table 11), F
7: 78-1-1 (Fig 3) have least reduction in germination per centage with value of 3.0 and F
7: 223-1-1 have maximum reduction in germination per centage with value of 92 (Fig 4) among checks lowest reduction was observed for check RBHP-38 (1.0%) and it was followed by IC-18563, DC 15 and DCS 47-1 with values 2.0, 3.0 and 4.0 respectively.
(Tomaz et al., 2007) found in some cases larval feeding effectively kills the embryo or feeds on the endosperm so that that the seed cannot be germinated.
The results considering seed damage per cent at 30, 45 and 75 days after release (DAR) of bruchids was minimum in highly resistant class, showing 18.16, 38.61 and 49.71% respectively (Table 6). In moderately resistant genotypes 25.99, 43.74 and 56.11 % at 30, 45 and 75 DAR, respectively. Least susceptible genotypes shown 28.78, 45.86 and 59.65% of damage at 30, 45 and 75 DAR respectively.
Whereas moderately susceptible genotypes shown 30.30, 45.63 and 61.59% of seed damage at 30, 45 and 75 DAR respectively. Highly susceptible genotypes exhibited more seed damage of 35.77, 47.83 and 65.68 % at 30, 45 and 75 DAR respectively. Among top 15 resistant F
7 segregants of stabilized lines (Table 7), F
7: 78-1-1 exhibited less seed damage of 13.41, 30.10 and 38.42% at 30, 45 and 75 DAR respectively (Fig 5) and F
7: 223-1-1 reported higher seed damage of 38.99, 52.71 and 64.42% at 30, 45 and 75 DAR (Fig 6). Among the checks, DC 15 shown moderate seed damage of 13.28, 24.01 and 28.56% at 30, 45 and 75 DAR respectively, whereas susceptible DCS47-1 registered 25.24, 64.04 and 73.72 % of seed damage at 30, 45 and 75 DAR respectively. Two rice bean checks (IC18563 and RBHP-38) registered minimum seed damage per cent, among these two IC18563 shown 3.48, 3.86 and 5.32% of damage at 30, 45 and 75 DAR respectively. Whereas, RBHP-38 registered 1.24, 3.73 and 6.40% of seed damage at 30, 45 and 75 DAR respectively and remained as minimum seed damaged check variety.
The results pertaining to the seed moisture reduction per cent (Table 10), the highly resistant class registered minimum seed moisture reduction of 1.72%, followed by moderately resistant (MR), least susceptible (LS), moderately susceptible (MS) and highly susceptible (HS) classes reported 2.86, 5.02, 5.32 and 6.17 per cent reduction respectively. While among the top 15 resistant lines (Table 11), F7: 78-1-1 have least reduction in moisture per cent with value of 1.33 per cent and among checks lowest reduction was observed for check RBHP-38 (0.64%) and it was followed by DC 15, IC-18563and DCS 47-1 with values 1.10, 1.13 and 1.99 per cent respectively.
The results on percent reduction in seedling length (Table 10) revealed that reduction is maximum in highly susceptible class with 17.74 per cent and it is followed with moderately susceptible, least susceptible, moderately resistant and highly resistant class with 13.54, 12.24, 5.18 and 1.31 per cent respectively. Among top 15 resistant lines (Table 11), the lowest per cent reduction was for the segregant F7: 59-3-1 followed by F7: 78-1-1. Among checks, RBHP-38, recorded minimum reduction in seedling length (0.54%) while checks, IC18563, DC 15 and DCS 47-1 shows1.12, 1.83 and 3.62 per cent reduction in seedling length respectively. The reduction in seedling length in highly susceptible plants is may be attributed to the depletion of cotyledon reserves due to the larval feeding of bruchid which later leads to the slower and reduced growth of the plants.
The results pertaining to seedling vigour index is shown in Table 10. In case of highly resistant varieties the reduction in seedling vigour index was less with value of 11.07 per cent compared to moderately resistant, least susceptible, moderately susceptible and highly susceptible types with values of 39.67, 73.28, 87.67 and 95.56 per cent reduction respectively. Among top 15 resistant F
7 stabilized lines (Table 11), F
7: 78-1-1 registered less reduction in seedling vigour index with the value of 8.28% and it was followed by F
7: 59-3-1 with 10.16%. Among the checks, the seedling vigour index was more reduced in check DCS 47-1 with 37.88% and it was followed by DC15, IC18563 and RBHP-38 with 15.08, 8.09 and 1.79 per cent reduction respectively. The reduction in seedling vigour index is mainly attributed to lowest value in seedling germination per cent and less seedling length in susceptible varieties since vigour is calculated by using both parameters.
Seed viability test was done using tetrazolium method and results with respect to per cent reduction among different classes of F
7 generations are represented in Table 10. There was considerable variation observed among the F
7 progenies. Highly resistant class noticed 5.00 per cent loss in seed viability and moderately resistant, least susceptible, moderately susceptible, highly susceptible classes noticed 16.02, 29.20, 37.14 and 47.13 per cent loss in seed viability, respectively in F
7 generations. The results with respect to per cent reduction in seed viability among top 15 resistant lines were given in Table 11. The progeny, F
7: 78-1-1 and F7: 59-3-1 recorded minimum (3.0%) loss in seed viability. Among the checks, rice bean accession RBHP-38 recorded least per cent loss (1.0%) in seed viability while, IC18563 recorded 4.0 % loss in seed viability. cowpea varieties DC 15 (MR), DCS 47-1 (MS), showed loss in seed viability of 14.0 and 22.0 per cent, respectively.
Yield is most important character and the genotypes showing minimum bruchid infestation and high yield
per se are desirable. Some of the segregants from highly resistant class registered the high yield. Among different classes highly resistant class registered highest yield
per se of 22.86 grams per plant, followed by moderately resistant class (21.97 grams per plant) (Table 8). Among top 15 resistant segregants F
7: 78-1-1 and F
7: 59-3-1 were proven to be high yielding segregants. Among checks the moderately resistant variety (DC 15) has shown 26.18 grams per plant and DCS 47-1 registered 22.80 grams per plant and both the rice bean checks RBHP-38 and IC18563 had registered 15.05 and 13.05 grams per plant respectively (Table 9).