Geminivirus resistance breeding in common bean.

Common bean (<i>Phaseolus vulgaris</i> L.) is among the most important food staples worldwide, mainly because of its relatively high protein content and other valuable nutritional qualities. Unfortunately, common beans are highly susceptible to plant viruses in general, including one of the largest families of plant viruses known as the <i>Geminiviridae</i>. These viruses, unlike most RNA plant viruses, possess a DNA genome that allows these pathogens to replicate in the nucleus of their plant host cells, thus, causing major damage to susceptible legume crops. Although some geminiviruses, belonging to two (<i>Mastrevirus</i> and <i>Curtovirus</i>) of the four genera that compose the <i>Geminiviridae</i>, can be transmitted by leafhoppers (Cicadellidae) to common bean, most geminiviruses that attack legumes belong to the genus <i>Begomovirus</i>, and are transmitted by the whitefly <i>Bemisia tabaci</i> (Genn.). In fact, the type species of this genus is bean golden yellow mosaic virus (BGYMV), which attacks over a million hectares of common bean grown in the lowlands and mid-altitude valleys of Central America, southern Mexico, the Caribbean region and northern South America. Another begomovirus, bean golden mosaic virus (BGMV), affects over two million hectares of common bean in Brazil, northern Argentina and the lowlands of Bolivia, in South America. In this region, bean dwarf mosaic virus (BDMV) has also caused the loss of thousands of hectares of highly valuable common bean genotypes in northwestern Argentina. In northwestern Mexico, thousands of hectares of common bean have been under the constant attack of a begomovirus related to a virus originally described in cucurbits, squash leaf curl virus (SLCV), in southwestern USA, currently known in Mexico as bean calico mosaic virus (BCaMV). Fortunately, none of these viruses is present in Eastern Africa, where the common bean is also a major food staple. Another Old World begomovirus reported to attack common bean both in the Old and New World, is tomato yellow leaf curl virus (TYLCV). This review describes the different breeding approaches followed since the 1970s to introduce resistance to begomoviruses infecting important legume crops, particularly common bean. This has been a challenging process, considering that no immune genotypes have been identified in more than 30000 common bean genotypes exposed to begomoviruses, such as BGMV or BGYMV.