Number of infected seeds
The mean number of seed/plant infected by pod suckers (
Riptortus linearis) is presented in Tabel 2. In controlled environment (P1), the mean number of seed/plant of healthy seed and infected seed were 363.5 and 581.0 seeds, respectively, or a total of 944.5 seeds. In uncontrolled environment (P0), the mean number of seed/plant of healthy seed and infected seed were 93.9 and 460.5 seeds, respectively, or a total of 554.4 seeds. This data indicated that the total seeds number in controlled environment (P1) was 70.4% higher than that in uncontrolled environment (P0).
In controlled environment (P1), mean number of seed/plant of healthy seed was 363.5 seeds which 38% lower than the infected seed (581.0 seeds). While in uncontrolled environment (P0), mean number of seed/plant of healthy seed was 93.9 seeds which 80% lower than the infected seed (460.5 seeds). This indicated that in uncontrolled environment (P0), the percentage number of infected seed to healthy seed was higher than that in controlled environment (P1).
The infestation intensity of seed/plants infected in controlled environment (P1) and in uncontrolled environment (P0) were 61.51% and 83.06%, respectively, suggested that infestation intensity of seed/plant infected in controlled environment (P1) was 26% lower than that in uncontrolled environment (P0). The mean effectiveness of control of od sucker was 35% which was based on infestation intensity of seed /plant infected in two environments (Tabel 2). This data suggested that, if there was no control, there would be a 65% reduction in number of seed /plant.
Based on infestation intensity in controlled environment (P1), there were three genotypes categorized as resistant (R) namely G1, G4 and G16 (Check variety Gema), six genotypes categorized as moderate resistant (MR) and seven genotypes (include G15 as check variety Anjasmoro) were categorized as susceptible (S). While in uncontrolled environment (P0), there were five genotypes categorized as resistant (R) namely G1 to G5, two genotypes as moderate resistant (MR) and nine genotypes (include G16 as check variety Gema) were categorized as susceptible (S) (Table 2).
In uncontrolled environment (P0), the percentage number of infected seed to healthy seed was higher than that in controlled environment (P1). The mean effectiveness of control of pod sucker was 35% which was based on infestation intensity of seed number/plant infected in two environments.
Seed weight infected per plant
The mean of seed weight/plant infected by pod suckers (
Riptortus linearis) is presented in Tabel 3. In controlled environment (P1), the mean of seed weight/plant of healthy seed and infected seed were 53.84 and 62.34 g, respectively, or a total of 116.18 g. In uncontrolled environment (P0), the mean of seed weight/plant of healthy seed and infected seed were 13.85 and 45.79 g, respectively, or a total of 59.64 g. This indicated that the total seed weight/plant in controlled environment (P1) was 95% higher than that in uncontrolled environment (P0).
In the present study, the percentage number of infected seed to healthy seed in uncontrolled environment (P0) was higher than that in controlled environment (P1). The mean effectiveness of control of pod sucking was 35% which was based on infestation intensity of seed number/plant infected in two environments. The total seed weight/plant in controlled environment (P1) was 95% higher than that in uncontrolled environment (P0). The study to pod sucking bug on soybean reported by
Krisnawati et al., (2016; 2017; 2018) showed that 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. On mung bean,
Indiati et al., (2021) reported that control application (L1) reduced pod damage by 48.50% and increased mung bean seed yield by 25%, compared to without control (L2).
The different level of resistance of genotype could be determined by different morphological characters. Plant morphological structures play a leading role in plant protection against insect pests as the first line of defense. Resistance to pod sucking pests associated with pod morphological factors (antixenosis) as well as antibiosis factors
(War et al., 2012).
Soybean morphological characters occured on leaves, stem and pod surface varied upon the variety which is the phenotypic characteristics. It was found that these characteristics has significant role on defense mechanism of soybean against pod feeding the insects. The resistance of soybean to pod sucking bug
Riptortus linearis was controlled by pod wall thickness and trichome density.
The different response of genotype to pod insect attack could be influenced by 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) and content of compounds or plant nutrients
(Halder and Srinivasan, 2007;
Sunitha et al., 2008). Crop damage was indirectly influenced by the high frequency of probing and oviposition
(Herlina et al., 2021). The thickness of the pod walls of the pegeon peas, the angle between the pods and the width of the pods showed a negative correlation with pod damage
(Halder and Srinivasan, 2011). The level of damage of soybean pod due to pod sucking bug followed the morphological characteristics on pods as number of trichomes, wide surface pod and number pod per nodes
(Hendrival et al., 2013; Jat et al., 2021; Krisnawati et al., 2022). The denser and longer trichomes on pods along with harder pod shells acts as a physical barrier in antixenosis resistance of soybean to the pod sucking bug
(Suharsono and Sulistyowati, 2012).