Opportunities for an improved potato late blight management in the Republic of Ireland: Field evaluation of the modified Irish Rules crop disease risk prediction model

Potato late blight remains the most significant disease threat of potato cultivation globally, often requiring expensive, time-consuming and environmentally unfriendly approaches to disease management. The goal of this research was to evaluate whether an estimation of potato late blight risk based on environmental factors can be reliably used to adjust the standard potato late blight management practices and the role of cultivar resistance under growing conditions and contemporary Phytophthora infestans populations in the Republic of Ireland. Using the modified Irish Rules model, it was possible to reduce fungicide usage by 58.7% on average, compared to current standard practices used by growers and without adversely compromising disease control and yield, with similar results achieved by the half dose programme. Host resistance levels were found to be correlated with a delay in the initiation of the epidemics, final foliar disease levels and reduction of fungicide usage. Disease levels on the highly resistant cultivars remained low and a clear selection pattern towards the P. infestans genotypes EU_13_A2 and EU_6_A1 was observed. An increase in the frequency of strains belonging to genotypes EU_13_A2 and EU_6_A1 was also observed to occur in the latter part of the trial growing seasons. Due to the increasingly dynamic nature of the population structure, associated with the continued evolution of the P. infestans population and the arrival of EU_36_A2 in the Republic of Ireland, routine population monitoring is required to ensure that potato late blight control strategies remain effective.

Mating Type and Aggressiveness of Phytophthora infestans (Mont.) de Bary in Potato-Growing Areas of Punjab, Pakistan, 2017–2018 and Identification of Genotype 13_A2 in 2019–2020

Samples of blighted potato leaves were collected from fields in six potato-growing districts of the Punjab Province of Pakistan in 2017–2018. A total of 149 isolates of Phytophthora infestans were obtained from six potato cultivars (Asterix, Barsenna, Burana, Caroda, Mazika, Sante). Of these isolates, 73% were A1 mating type, 23% were A2 mating type and 4% were self-fertile. Both mating types of P. infestans occurred in all six districts sampled, but in every case, the A1 mating type predominated. The foliar aggressiveness of 104 of these isolates (weakly pathogenic isolates were excluded) was tested on detached leaflets of potato cv. 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. There was no difference in CAI between isolates obtained from different districts or cultivars. 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. 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. 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. This is the first report of EU_13_A2 from Pakistan. The implications for potato late blight management in the Punjab are discussed.

Governing a Collective Bad: Social Learning in the Management of Crop Diseases

There has been strong research interest in designing and testing learning approaches for enhancing and sustaining the capacity of communities to manage collective action problems. Broadening the perspective from well-known social learning approaches in natural resource management, this study explores how social learning as a communicative process influences collective action in contagious crop disease management. A series of facilitated discussion and reflection sessions about late blight management created the social learning space for potato farmers in Ethiopia. Communicative utterances of participants in the sessions served as the units of analysis. The study demonstrates how and to what extent social learning, in the form of aligned new knowledge, relations and actions occurred and formed the basis for collective action in the management of late blight.