A new isolate of Pepper huasteco yellow vein virus (PHYVV) breaks geminivirus tolerance in tomato (Solanum lycopersicum) commercial lines

Nowadays, diseases caused by geminiviruses have become the limiting factor for tomato production in tropical and subtropical regions worldwide, including Mexico. Development of genetic resistance by classical genetic breeding consisting of the introgression of resistance genes from wild-type tomatoes to domesticated species is considered the best solution for virus management. Major efforts have been performed to develop tomato lines tolerant to the monopartite geminivirus Tomato yellow leaf curl virus (TYLCV), which is the most damaging, most widely distributed, and most extensively studied geminivirus. However, besides this monopartite geminivirus, many tomato-infecting bipartite begomoviruses, such as Pepper huasteco yellow vein virus (PHYVV), are known. PHYVV is an endemic and widely distributed species in Mexico detected during the early 1990s that infects tomato, but viral titers are low and infected plants remain symptomless. Recently, an outbreak of symptoms resembling TYLCV infection was detected in northern Mexico tomato fields, where tomato commercial lines tolerant to TYLCV are cultivated. Molecular and phylogenetic analysis of a survey of symptomatic tomato and pepper plants revealed the presence of a new strain of PHYVV. Using agroinfectious clones, commercial tolerant tomato hybrids, available in Mexico, were challenged against TYLCV or PHYVV infection. Symptomatology assessment and quantitative PCR (qPCR) viral titer quantification showed that all lines remained tolerant against TYLCV; however tolerance was disrupted, with PHYVV displaying differential symptomatology in all tested lines. The presence of a new strain of PHYVV pinpoints the importance of research focused on the generation of new wide-spectrum resistant lines against geminivirus.