Resistance to pests and disease
The intensity of armyworm infestation on the tested soybean lines showed difference categories ranged from very susceptible to resistant (Table 2). Two soybean lines AGm-29-3-2 and DM-122-35-17 showed resistant (R) level against armyworm pests which were equivalent to that of Grobogan check variety and more resistant than that of Dering 1 check variety which was classified as moderately resistant (MR) (Table 2). One soybean line (DG-91-8) and eight soybean lines showed resistant (R) and moderately resistant (MR) categories, respectively to pod suckers (
Riptortus linearis). While the check varieties Grobogan and Dering 1 showed highly susceptible (HS) and moderately resistant (MR), respectively (Table 2).
Three soybean lines (DG-91-8, DG-100-33-15 and DM-122-35-17) showed resistant (R) category to pod borer (
Etiella zinckenella). While the check varieties Grobogan and Dering 1 showed highly susceptible (HS) and susceptible (S) categories, respectively (Table 2). All genotypes showed moderately resistant (MR) category to leaf rust disease
(Phakopsora pachyrhizi).
There was no soybean line showed resistant (R) category based on resistant level to three major pests above. Soybean line DG-91-8 showed resistant (R) category to pod borer and pod sucker, while DM-122-35-17 showed resistant (R) category to army worm and pod borer. Three soybean lines (TGm-161-25-10, AB-157-41-22 and DG-240-44-25) showed moderately resistant (MR) category to three major pest above (Table 2). Two soybean lines (DG-91-8 and DG-240-44-25) showed improvement on resistance level to three major pest above compared to check varieties Grobogan and Dering 1 as their parents in their pedegree crosses (Table 1).
Based on the value of the percentage of seed damage, there were two resistant genotypes, however, based on the value of the percentage of pod damage, only one genotype showed a resistant level that was G511H/Anjasmoro//Anjasmoro-2-8. A very high natural population of pod sucking bug was recorded in the field with the average number of damaged pod in full protection environment (L1) and insecticide control until 50 dap (L2),
i.e. 41.45% and 60.16%, respectively. Genotype of G511H/Anj//Anj-2-8 was consistently resistant to pod sucking bug both in L1 and L2
(Krisnawati et al., 2016; 2017; 2018).
Seed yield and yield components
The seed yield of 13 soybean lines ranged from 2.11 to 2.76 t/ha. Seven lines showed higher seed yield than check varieties (Dering 1 and Grobogan). Two highest yielding line (DG-91-8 and DG-99-32-14) had 15% higher seed yield than check variety Dering 1 (2.41 t/ha). These two lines also had higher seed size (100 seeds weight) and pod number/plant (Table 3). Soybean line DG-91-8 also showed resistant (R) category to pod borer and pod sucker (Table 2).
Protein and fat concentrations
The range of protein and fat concentrations of soybean lines are presented in Table 4. The highest protein and fat concentrations was showed by TGm-288-38-19 (41.47%) and AB-157-41-22 (19.74%), respectively. These concentrations were higher than the check varieties Dering 1 and Grobogan.
Correlation among characters
The correlation among characters of soybean lines are presented in Table 5. The correlation between protein content and fat concentration shows a significant negative value, but did not show a significant correlation with the intensity of infestation of the three pest types. Fat concentration shows a significant positive correlation with leaf rust disease. Pod suckers showed a significant positive correlation with the intensity of pod borer infestation, indicating that these two types of pests had the same preference for soybean pods. Seed yield and number of pods showed significant positive correlation value. This finding agrees with the study reported by
San et al., (2022) that there was a negative relationship between biological attributes of
H. armigera and protein content in different chickpea genotypes.
The different response of genotype to pod borer attack could be influenced by various factors, including pod morphology (wall thickness of pods, number of pods/cluster, angle between pods in one cluster, trichome pods, length, density and position of trichome pods, pod length and pod width). In addition to differences in pod morphology, the content of compounds or plant nutrients can also affect the level of pod borer attack
(Sunitha et al., 2008; Halder and Srinivasan 2007;
2011).
Plant resistant to insect pest may expressed in a morphological characters such as dense and rigid, irregular trichome structure, the thicker leaves and stem and harder pod shell (
Suharsono 2009;
Suharsono and Sulistyowati 2012). Resistance to pod sucking pests associated with pod morphological factors (antixenosis) as well as antibiosis factors
(Haq et al., 2003; War et al., 2012). The angle between the pods and the widt h of the pods showed a negative correlation with pod damage of pegeon pea genotypes
(Halder and Srinivasan 2011). The level damageof soybean pod do tue pd sucking bug on soybean varieties Kipas Merah and Anjasmoro determined by the number of trichomes, wide surface pod and number pod per nodes
(Hendrival et al., 2013).
