Biotechnology-assisted development of virus-resistant varieties and populations of squash for climate change adaptation

Date

2023

Abstract

Squash leaf curl is a serious disease of squash caused by Squash leaf curl virus (SLCV), a begomovirus, transmitted by whiteflies, Bemisia tabaci Genn. Surveys conducted in 24 provinces in the country showed the presence of SLCV in mixed infections along wit other viruses including Papaya ringspot virus (PRSV-w), Zucchini yellow mosaic virus (ZYMV), Cucumber mosaic virus (CMV) and Cucurbit aphid-borne yellows virus (CABYV). Majority of the samples exhibited varying symptoms of mosaic, vein banding, veinenation, leaf curling, bistering, mottling, and leaf distortion, while some samples displayed only mild apparently healthy appearance. Virus infection in the collected fields ranged from 5-100% and was associated with aphids and whitefly infestations. The incidence of SLCV was 67% and was observed to be the most commonly occurring virus throughout the region surveyed. Multiple sequence alignment of the 1.3 kb products of the C1 partial, IR, C4, AV2, CP partial genes of the different local SLCV isolates showed 86.5-99% identified among isolates. Four possible SLCV strains were identified based on virus strain demarcation of less than 92% as follows; 1 SLCV isolates from Region 2 (Quirino and Nueva Viscaya) and Region 3 (Nueva Ecija and Bataan) having low sequence identity with any of the isolates collected from other provinces of Luzon, Visayas and Mindanao; 2) Benguet isolate with high sequence similarity of 94.2 to 94.5% to the Ilocos Sur isolates only but low sequence similarities of 87.3-92.9% with the rest of SLCV isolates; 3)the Davao isolates with only 90-92.8% identity with the rest of the Mindanao isolates and low sequence identity of 87.3-92.9% with Cebu and other Luzon isolates; and 4)the Laguna and Cavite isolates having high sequence similarities with all other SLCV isolates of Palawan, Camarines Sur, Albay, Cebu and the rest Mindanao. When aligned with the different SLCV Philippines strains in the GenBank, the local isolates clustered into 3 groups namely; SLCV Phil-Nueva Ecija, SLCV Phil-Batangas and SLCV-Phil-Laguna. The infectious cDNA clones of SLCVDNA-A and DNA-A and DNA-B from Laguna isolate have been constructed and made infectious by agrinoculation into healthy seedlings of squash. Seedlings developed the typical leaf curl symptoms 3-4 weeks after agroinoculations with the mixed suspension of SLCV-DNA-A and DNA-B only but not with either SLCV DNA-A or SLCV DNA-B clones. Fourteen out of 27 AVRDC accessions displayed resistance to either ZYMV or PRSV-W in greenhouse test. One accession, AVPU 1318 was found resistant to ZYMV but moderately resistant to PRSV-W while 5 accessions namely: AVPU 1309, 1314, 1213 sib, AVPU 1223-3 OP and AVPU 1232-5(X) have moderate resistance to both viruses. Among the 47 local squash breeding lines and accessions evaluated against the 2 viruses in greenhouse test, 5 lines were moderately resistant to ZYMV, 7 lines were moderately resistant to PRSV, while 2 of these lines were moderately resistant to both viruses. Four more squash breeding lines were found promising in greenhouse screening trial in 2014. One line (131538) showed moderate resistance to both ZYMV and PRSV-W. The 3 other breeding lines namely: 13154, 131562 and 131564 were moderately resistant to either ZYMV or PRSV-W but were susceptible to SLCV. Field evaluation of some AVRDC lines and accessions against viruses showed several AVPU lines with resistance to the viruses but most of the accessions were not adapted to the hot, humid tropical conditions since fruit setting is low and most of them were highly susceptible to the cucurbit beetle (Aulocophora similis). The AVPU lines with virus resistance were crossed to the local selections to recombine the desirable traits from the two groups of germplasm. Forty five F1 crosses were generated and the segregating lines were evaluated with the selected plants selfed or sibbed for generation advancement of the second and third year of the project. A total of more than 700 breeding lines were generated. Selection between and within the lines started at F sub 3 based on virus resistance in the field, vigor, fruit weight and thickness and fruit eating quality. By the end of the project, 33 promising line were selected which will be subjected to yield trial to determine their performance in comparison with the check varieties.

Document Type

Article

Pages /Collation

116 leaves

En – AGROVOC descriptors

SQUASHES; VIRUSES; DISEASE RESISTANCE; ENVIRONMENTAL IMPACT; CLIMATIC CHANGE; LEAF CURLS; SYMPTOMS; PROGENY; SELECTION

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