Sexual recombination can lead to greater variability, rendering the population more adaptable and generating more aggressive genotypes, which may be fungicide-resistant (Drenth et al. 2000), cause early infections and affect the population structure (Fry 2008). Where both mating types are present in the same field, sexual recombination may occur resulting in formation of sexual oospores which can survive in soil for several years (Turkensteen et al. The A2 mating type was first reported outside Mexico by Hohl and Iselin ( 1984), and now, both mating types occur in most potato-producing regions worldwide (Fry et al. Until the 1980s, the A2 mating type had been found only in Mexico where Gallegly and Galindo ( 1958) showed that both mating types were present elsewhere, only the A1 mating type had been identified. infestans is a heterothallic oomycete with two mating types, A1 and A2.

2004), and even with low infection levels, the crop may be unsuitable for storage (Fernández-Northcote et al. It is one of the main limiting factors for potato production in the world, and if the disease is not controlled, losses can reach 100% (Ghorbani et al. Late blight of potato caused by Phytophthora infestans (Mont.) de Bary is the most devastating disease affecting the crop worldwide in terms of both quality and quantity of yield (Nowicki et al. While potato consumption has been declining in Europe and North America, it has been steadily increasing in the developing world now, more potato production takes place in developing countries than in the developed world and potatoes have an important role in food security of developing countries (Wijesinha-Bettoni and Mouillé 2019). Potatoes grow in a wide range of habitats from sea level to 4000 m altitude and from 47° S to 65° N latitude (Hijmans 2001). 2019) its tubers are a globally important dietary source of starch, protein, antioxidants and vitamins (Burlingame et al. Potato ( Solanum tuberosum L.) is the most important vegetable crop worldwide and the third most important food crop after wheat and rice (Jansky et al. The implications for potato late blight management in the Punjab are discussed. This is the first report of EU_13_A2 from Pakistan. While it was not possible to test the isolates collected in 2017–2018, genotyping of samples collected in 2019–2020 showed the widespread occurrence of the EU_13_A2 clonal lineage in the same districts of Pakistan and supported this hypothesis. It may be that the A2 isolates belonged to an aggressive clonal lineage such as 13_A2 that has been reported in other countries in the region. The A2 mating type isolates had significantly greater CAIs than A1 isolates but this does not imply a genetic linkage nor a general association between mating type and aggressiveness. There was no difference in CAI between isolates obtained from different districts or cultivars. Caroda, and a composite aggressiveness index (CAI) calculated from lesion area (measured after 10 days), latent period and infection frequency was used to compare isolates.

The foliar aggressiveness of 104 of these isolates (weakly pathogenic isolates were excluded) was tested on detached leaflets of potato cv. infestans occurred in all six districts sampled, but in every case, the A1 mating type predominated. Of these isolates, 73% were A1 mating type, 23% were A2 mating type and 4% were self-fertile. A total of 149 isolates of Phytophthora infestans were obtained from six potato cultivars (Asterix, Barsenna, Burana, Caroda, Mazika, Sante). Samples of blighted potato leaves were collected from fields in six potato-growing districts of the Punjab Province of Pakistan in 2017–2018.

Phytophthora tomato