Antixenotic and allelochemical resistance traits of watermelon against Bactrocera cucurbitae in a hot arid region of India
Keywords:
flavonoid, alkaloid, phenol, tannin, ‘Asahi Yamato’, ‘BSM-1’Abstract
Host plant resistance is an important component of integrated pest management of the melon fly, Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae). We studied various antixenotic and allelochemical traits in the fruit for 15 varieties/genotypes of watermelon Citrellus lanatus (Thunb.) Matsumara & Nakai (Cucurbitales: Cucurbitaceae) in relation to resistance against B. cucurbitae under field conditions in a hot arid region of India. Results showed significant differences in tested varieties/genotypes in levels of fruit infestation and larval density per fruit. The varieties/genotypes ‘Asahi Yamato’ (12.73%), ‘AHW/BR-16’ (15.10%), and ‘Thar Manak’ (18.27%) were found to be resistant; ‘Durgapura Lal’ (23.03%), ‘Sugar Baby’ (26.67%), ‘AHW/BR-12’ (29.73%), ‘Arka Manik’ (34.15%), ‘Charleston Gray’ (38.70%), ‘AHW-65’ (35.80%), and ‘AHW-19’ (48.97%) were found to be moderately resistant; and ‘IC 582909’ (53.18%), ‘AHW/BR-60’ (55.52%), ‘BSM-1’ (59.10%), ‘AHW/BR-137’ (60.58%), and ‘AHW/BR-9’ (67.37%) were found to be susceptible to fruit fly infestation. Significant positive correlation (r = 0.99; P < 0.01) was observed between percentage fruit infestation and larval density per fruit. Percentage fruit infestation and larval density per fruit were significantly and positively correlated with fruit length (r = 0.57 and 0.55, respectively) and with days to first fruit harvest (r = 0.75 and 0.76, respectively), but negatively correlated with length of ovary pubescence (r = −0.91 and −0.91, respectively), rind hardness (r = −0.86 and −0.87, respectively), and rind thickness (r = −0.77 and −0.75, respectively). Maximum variation in fruit infestation and larval density were explained by length of ovary pubescence (82.5 and 83.6%, respectively) followed by fruit length (4.3 and 3.0%, respectively) and rind thickness (3.2 and 2.0%, respectively). Free amino acid content was lowest in the resistant ‘Asahi Yamato’ and highest in the susceptible ‘BSM-1’, whereas the contents of phenols, tannins, total alkaloids, and flavonoids were highest in resistant and lowest in susceptible varieties/genotypes. Flavonoid and total alkaloid contents explained 88.4 and 92.0%, respectively, of the total variation in fruit fly infestation and in larval density per fruit.
Resumen
La resistencia de las plantas hospederas es un componente importante para el manejo integrado de plagas de la mosca del melón, Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae). Estudiamos varios características antixenoticas y de aleloquímicos en el fruto de 15 variedades/genotipos de sandía Citrellus lanatus (Thunb.) Matsumara y Nakai (Cucurbitales: Cucurbitaceae) en relación a la resistencia contra B. cucurbitae en condiciones de campo en una región árida y caliente de la India. Los resultados mostraron diferencias significativas en las variedades/genotipos probados en los nivelesde infestación de la fruta y de la densidad de larvas por fruto. Las variedades/genotipos ‘Asahi Yamato’ (12,73%), ‘AHW/BR-16’ (15,10%) y ‘Thar Manak’ (18,27%) resultaron ser resistentes; ‘Durgapura Lal’ (23,03%), ‘Sugar Baby’ (26,67%), ‘AHW/BR-12’ (29,73%), ‘Arka Manik’ (34,15%), ‘Charleston Gray’ (38,70%), ‘AHW-65’ (35,80%) y ‘AHW-19’ (48,97%) resultaron ser moderadamente resistente; y se encontraron ‘IC 582909’ (53,18%), ‘AHW/ BR-60’ (55,52%), ‘BSM-1’ (59,10%), ‘AHW/BR-137’ (60,58%) y ‘AHW/ BR- 9’ (67,37%) susceptibles a la infestación de mosca de la fruta. Se observó una correlación positiva significativa (r = 0,99; P < 0,01) entre el porcentaje de infestación de fruta y la densidad de larvas por fruto. Se correlacionaron significativamente y positivamente el porcentaje de infestación de frutas y la densidad de larvas por fruto con la longitud del fruto (r = 0,57 y 0,55, respectivamente) con el número de días hasta la primera cosecha de la fruta (r = 0,75 y 0,76, respectivamente), pero fueron negativamente correlacionados con la duración de la pubesencia de ovario (r = −0,91 y −0,91, respectivamente), la dureza de corteza (r = −0,86 y −0,87, respectivamente), y el grueso de la corteza (r = −0,77 y −0,75, respectivamente). Se explica la variación máxima de la infestación de frutas y la densidad larval por la longitud de pubescencia del ovario (82,5 y 83,6%, respectivamente) seguido de la longitud del fruto (4,3 y 3,0%, respectivamente) y el grueso de la corteza (3,2 y 2,0%, respectivamente). El contenido de aminoácidos libres fue más bajo en el resistente ‘Asahi Yamato’ y más alto en el susceptible ‘BSM-1’, mientras que el contenido de fenoles, taninos, alcaloides totales y flavonoides fue más alto en las variedades/genotipos resistentes y menor en las variedades susceptibles. El contenido de alcaloides y flavonoides totales explicaron el 88,4 y 92,0%, respectivamente de la variación total de la infestación por la mosca de la fruta y de la densidad de larvas por fruta.
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