Chili peppers (Capsicum annuum L.) are an economically important crop worldwide. Pepper yellow leaf curl Thailand virus (PepYLCTHV), a Begomovirus causing yellow leaf mosaic disease of chili pepper, has been reported to incur 95% economic loss under epiphytotic conditions. Thirty-one chili genotypes were screened for resistance to PepYLCTHV disease through inoculation using 10–15 viruliferous whiteflies per plant. We purified two resistant lines (PEP6 and PEP12) through four generations of selfing and selection. At 28 days after inoculations, two chili genotypes (PEP6 and PEP12) had low disease severity and percentage of disease incidence (DI) compared to four susceptible checks, viz., Yodsonkeam80, Homsupan, Huareau12, and Pong Charian, which had a disease severity score of 5 with 100% DI. Thirty initial plants of PEP6 showed an average disease severity of 3.64 with 69.33% DI, and PEP12 showed an average disease severity of 3.83 with 77.67% DI. From these populations, we selected nine highly resistant plant of PEP6 and seven plants of PEP12 having a disease severity of 0 through pure-line selection for four selfing generations. The ratio of resistance (R) to susceptibility (S) consequently decreased. In PEP6, the ratio decreased from 1R:2S to 1R:1S, while in PEP12 the ratio decreased from 1R:3S to 1R:1S. These lines have potential for release as resistant lines for improving chili pepper resistance to PepYLCTHV and for developing makers associated with the resistant trait.

Chili peppers (Capsicum annuum L.) are economically important crop worldwide. Pepper yellow leaf cure Thailand virus (PepYLCTHV), a Begomovirus causing yellow leaf mosaic disease of chili pepper has been reported to damage 95% economic loss under favorable epidemic conditions. Thirty-one chili genotypes were screened for resistance to PepYLCTHV disease through challenge inoculation using 10-15 viruliferous whiteflies per plant. We purified two resistant lines (PEP6 and PEP12) through four generations of selfing and selection through challenged inoculations. At the 28 days after inoculations two chili genotypes showed symptoms less based on disease severity and percentage of disease incidence of 30 plants PEP6 showed a disease severity 3.64 with 69.33 % DI and PEP12 showed a disease severity 3.83 with 77.67 % DI. PEP6 and PEP12 were selected for pure-line development for four cycles.Both varieties showed an increase in percentage of the resistant plant 12.78 % and 16.77 %, respectively. These lines have potential for release as resistant lines for improvement chili pepper resistance to PepYLCTHV and for developing maker associated with the resistant trait.

This study investigated the genetics of resistance to Pepper yellow leaf curl virus (PepYLCTHV) in advanced lines of chili peppers (Capsicum annuum) and generated new chili pepper populations resistant to PepYLCTHV disease. Experiments were conducted in three phases between May 2020 and October 2024 at three locations in Thailand. Three crosses were developed, involving PepYLCTHV-resistant (PEP6) and susceptible Jindanil 80 (JD), PP0437-7506, and Yodsonkeam 80 (YS) parents; PEP 6 was used as a common male parent. The segregation of resistant and susceptible plants was studied in F₂, F₃ and F₅ generations, and yield components of selected F₅ lines were recorded and analyzed. The parental line PEP6 exhibited a segregation ratio of resistant (R) to susceptible (S) plant (1R:1.5S), while PP0437-7506 fit a 1R:15S ratio. The F₁ generations were completely susceptible, confirming that resistance is a recessive trait. The resistant-to-susceptible ratio from F₂ to F₅ generations was increased, suggesting that advanced-generation selection for resistance is effective. The population of YS/PEP6 showed an increase in resistance across generations, with ratios changing from 1R:15S in the F₂ to 1R:1S in the F₅. These results suggest that resistance to PepYLCTHV was under the control of multiple recessive genes. Evaluations of new breeding lines regarding disease severity and index (DI%) confirmed that the resistant parent PEP6 had low disease severity (1.1) and DI% (22%). In contrast, commercial and local varieties were highly susceptible. Two promising F₅ lines, PF2 and PF8, derived from PEP6 developed during this study, displayed high levels of resistance with low DI% values of 24.67% and 18.67%, respectively. These lines are improved sources of PepYLCTHV-resistant chili pepper for further evaluation and direct release as PepYLCTHV disease-resistant cultivars in the Thai market segment and could be used as an improved source of resistance for breeding programs.