In the present investigation, out of 200 inter sub-specific lines screened, eleven lines were recorded as resistant (< 20% seed damage) (data not shown). However, three resistant lines with less seed damage 17.00% (GGISC 124, GGISC 150) and 18.00% (GGISC 140) were further taken for bruchid confirmation screening and also for GC-MS analysis along with a susceptible check [VBN (Gg) 2].
During confirmation screening, the bruchid screening parameters were recorded in three resistant lines and a susceptible check and are presented in Table 1. All the parameters recorded in resistant lines showed significant difference when compared to susceptible check. Among the lines, initial seed weight for 50 seeds was 1.21 g (GGISC 124), 1.26 g (GGISC 140), 1.54 g (GGISC 150) and 1.86 g [VBN (Gg) 2]. Three resistant lines showed less weight loss and recorded final seed weight (after 30th day) of 1.07 g (GGISC 124), 1.10 g (GGISC 140) and 1.37 g (GGISC 150). VBN (Gg) 2, a susceptible line showed the highest reduction in seed weight and recorded the final weight of 0.76 g.
The days to first adult emergence was prolonged in resistant lines when compared to VBN (Gg) 2. The days to first adult emergence recorded was 24 days (GGISC 124, GGISC 140, GGISC 150) and was only 20 days in susceptible check. The mean developmental period was longer in resistant lines when compared to VBN (Gg) 2. The mean developmental period recorded was 27 days (GGISC 140), 26 days (GGISC 124, GGISC 150) and 23 days in the susceptible check VBN (Gg) 2.
Soumia et al., (2017) also reported longer developmental period in resistant lines when compared to susceptible lines in greengram. The weight of 10 pairs of bruchids were 45.00 mg in VBN (Gg) 2 and however sufficient number of bruchids was not emerged in the specified time (30 days) inorder to record weight of the bruchids. The bruchids emerged from resistant lines were observed as malformed and small in size than in the susceptible lines.
Samyuktha et al., (2020) reported that the resistant genotypes expressed the antibiosis mechanism against bruchid infestation and caused the malformation and death of grub in greengram. The number of adults emerged on 30
th day in resistant lines were nine, whereas in susceptible check 50 adults were emerged (Table 1).
Sarkar and Bhattacharyya (2015) also reported high bruchid infestation in susceptible lines of greengram.
In the present study, damage assessment parameters
viz., weight loss per cent of the seed, susceptibility index and seed damage were worked and are presented in Table 1. The three resistant lines recorded less weight loss per cent of seed
viz., 11.59 per cent (GGISC 124), 12.41 per cent (GGISC 140) and 11.37 per cent (GGISC 150), whereas susceptible check [VBN (Gg) 2] recorded the highest seed weight loss of 59.15 per cent (Table 1).
Seram et al., (2016) and
Harshitha et al., (2022) reported less weight loss per cent of seed in bruchid resistant lines of greengram.
The three resistant lines recorded susceptibility index less than 0.050 (resistant category)
viz., 0.046 (GGISC 124), 0.047 (GGISC 140) and 0.048 (GGISC 150), whereas the susceptible check [VBN (Gg) 2] recorded the susceptibility index of 0.085 (Table 1).
Neupane et al., (2016), Ghosh et al., (2022) and
Harshitha et al., (2022) have also used the susceptibility index and weight loss per cent for determining the level of bruchid resistance in greengram and were found to be high in susceptible lines.
Seed damage per cent on 30
th day was less than twenty per cent in three resistant lines
viz., 17.00 per cent (GGISC 124, GGISC 150) and 18.00 per cent (GGISC 140), whereas the susceptible check (VBN (Gg) 2) reached 100 per cent adult emergence on 30
th day of inoculation (Table 1).
Harshitha et al., (2022) also reported the 100 per cent adult emergence on 30
th day of inoculation in VBN (Gg) 2.
Sarkar and Bhattacharyya (2015) and
Soumia et al., (2017) reported that in susceptible varieties of greengram, the susceptibility index was more than 0.050 and the seed damage was more than 40 per cent.
Soumia et al., (2017) reported that the reduction in adult emergence is an indication of the presence of antibiosis factors in seed that results in the prolongation of developmental period of bruchid in greengram.
The resistant lines
viz., GGISC 124, GGISC 140, GGISC 150 and susceptible check VBN (Gg) 2 were subjected to GCMS analysis for identifying the chemical compounds responsible for resistance to
C. chinensis. The data generated by gas chromatography showed that the composition of the various chemical compounds were present in three resistant lines and a susceptible check. The GC-MS chromatogram plot of the resistant lines GGISC 124, GGISC 140, GGISC 150 and susceptible check VBN (Gg) 2 obtained are shown in Fig 1 to 4, respectively. In the present study, a total of forty bioactive compounds were observed in GC-MS analysis. Among them, seven compounds showed difference in peak area (%), molecular formula, molecular weight and retention time (min.) (Table 2).
Among the seven compounds identified four compounds
viz., Hexadecanoic acid, methyl ester; n-Hexadecanoic acid; 9, 12-octadecadienoic acid (Z, Z) and Octadecaenoic acid were observed in all the four lines including susceptible check with some difference in per cent peak area. The compounds
viz., Hexadecanoic acid, methyl ester; n-Hexadecanoic acid and 9, 12-octadecadienoic acid (Z,Z) were reported while studying bruchid resistant and susceptible lines in chickpea
(Reddy et al., 2021) and in blackgram
(Ragul et al., 2022) through GC- MS analysis.
Bharathithasan et al., (2021) also reported insecticidal property of Octadecaenoic acid against insect pest of Areca nut.
Among the seven compounds identified, three compounds were found to distinguish the resistant (GGISC 124, GGISC 140, GGISC 150) and susceptible check [VBN (Gg) 2]. The first compound 9, 12-Octadecadienoic acid, methyl ester was observed with the peak area of 1.032 per cent, 2.960 per cent and 3.063 per cent in the resistant lines GGISC 124, GGISC 140 and GGISC 150, respectively with retention time of 24.94 minutes (Table 2). The second compound Hexadecanoic acid, 1-(hydroxymethyl)-1, 2-ethanediyl ester was reported with the peak area of 0.254 per cent, 1.838 per cent and 0.487 per cent in the resistant lines GGISC 124, GGISC 140 and GGISC 150, respectively with the retention time of 26.29 minutes (Table 2). The third compound Hexadecanoic acid, 2-oxiranyl methyl ester was identified in the peak area of 5.804 per cent, 3.390 per cent and 2.862 per cent in the resistant lines GGISC 124, GGISC 140 and GGISC 150, respectively with the retention time of 28.45 minutes (Table 2). The compound 9, 12- Octadecadienoic acid, methyl ester was reported against bruchid infestation in chickpea
(Reddy et al., 2021). Hexadecanoic acid, 1-(hydroxymethyl)-1, 2-ethanediyl ester and Hexadecanoic acid, 2-oxiranyl methyl ester were known to have insecticidal properties against insect pest of Areca nut
(Bharathithasan et al., 2021). Therefore, in the present study, 9, 12- Octadecadienoic acid, methyl ester; Hexadecanoic acid, 1-(hydroxymethyl)-1, 2-ethanediyl ester and Hexadecanoic acid, 2-oxiranyl methyl ester were identified as the compounds responsible for bruchid (
Callosobruchus chinensis) resistance in greengram.