Host plant resistance in cowpea (vigna unguiculata (L.) Walp) against Aphis craccivora Koch (Hemiptera: Aphididae)

Abstract

The present study titled ‘Host plant resistance in cowpea (Vigna unguiculata (L.) Walp) against Aphis craccivora Koch (Hemiptera: Aphididae)’ aimed to assess the resistance or susceptibility of cowpea germplasms to A. craccivora and to identify the mechanisms underlying this resistance through antixenosis, antibiosis and biochemical analyses. Field screening of thirty-two cowpea germplasms was conducted from January to March 2025 at Instructional Farm I, College of Agriculture, Padannakkad, under natural infestation conditions. In the field evaluation, Kashi Nidhi (13.27) recorded highest number of aphids per 2.5 cm shoot and Kashi Gauri the lowest (0.15). Other insect pests such as stem fly, leaf miner, leaf roller and cow bug were also observed, though significant differences were noted only in stem fly and leaf miner incidence. Stem fly damage was highest in Lola (6.33) and lowest in Konkan Wali (0.00), while leaf miner incidence was greatest in TCR 57 (1.13) and lowest in Lola, KAU Sreenandha, TCR 53, TCR 36 and Maharashtra local variety 3(0.00). Despite these variations, no visible foliar or floral damage attributable to aphids was recorded, and population differences alone were insufficient to categorise the entries into resistant/ susceptible under field conditions. In that context, cage screening was conducted that provided a clearer separation of germplasm response to A. craccivora. Seedling survival after release of aphids was found to be highest in Arka Samrudhi (41.67) and lowest in Geethika, Karkoonthal Payar and Maharashtra Local variety 3 (15). Damage assessments showed a comparable pattern, with Geethika, Karkoonthal payar and Maharashtra local variety 3 recording the highest cumulative scores (5.00) and Arka Samrudhi (2.11) the lowest. None of the germplasms were categorized as highly resistant or resistant; five were classified as moderately resistant (MR), nine as moderately susceptible (MS), and eighteen as highly susceptible (HS). Two germplasms from each category - MR (Anaswara, Arka Samrudhi), MS (Konkan Wali, Phule Pandhari), and HS (Geethika, Karkoonthal payar) were selected for studying host plant resistance mechanisms. Antixenosis (non-preference) studies on the six selected germplasms revealed that mean number of aphids migrated per plant was highest in highly susceptible 98 Geethika (90.50) and lowest in moderately resistant Arka Samrudhi (23.25). The selected germplams showed an effect on growth, reproduction and survival of the aphids. The mean weight of 10 aphids and number of progeny per aphid were maximum in Geethika (7.32 mg and 21.00, respectively) and the mean survival period was highest in Karkoonthal payar (10.25 days), whereas Arka Samrudhi recorded the lowest values for all three parameters (4.68 mg, 6.75 progeny, and 6.75 days, respectively). The results indicate that highly susceptible genotypes promote aphid development and survival whereas moderately resistant types suppress growth, reproduction and longevity. Biochemical and nutrient estimation of the selected MR and HS germplasms showed that nitrogen, phosphorus, potassium and protein contents were highest in Karkoonthal payar (5.45%, 0.48%, 4.72% and 340468.75 µg g⁻¹ respectively) and lowest in Arka Samrudhi (3.35%, 0.24%, 2.66%, 209531.25 µg g⁻¹respectively). The total phenol content was highest in Anaswara (381.56 µg g-1) and lowest in Geethika (186.21µg g-1), and both flavonoid and terpenoid levels were highest in Arka Samrudhi (1326.26 µg g-1, 4775.83 µg g-1) and lowest in Karkoonthal payar (496.43 µg g-1, 2309.24 µg g-1). The highly susceptible Geethika showed maximum plant height (142.80 cm) and number of primary branches (7.75), while moderately susceptible Phule Pandhari (29.15 and 3.00 respectively) recorded the lowest values. Number of leaves/plant were highest in Anaswara (17.75) and lowest in Phule Pandhari (9.25). Trichome density was greatest in Karkoonthal payar (21.50/cm leaf margin) and lowest in Anaswara (14.75/cm leaf margin), whereas trichome length was longest in Anaswara (0.42 mm) and shortest in Karkoonthal payar (0.10 mm). In the present study, principal component analysis clearly separated resistant and susceptible germplasms, with Arka Samrudhi and Anaswara clustering opposite Geethika and Karkoonthal payar, showing that resistance was associated with higher biochemical defenses and longer trichomes, whereas susceptibility clustered with elevated nutrient levels and stronger aphid performance traits.