Molecular Microbiology Research 2024, Vol.14, No.4, 181-187 http://microbescipublisher.com/index.php/mmr 184 5 Control Strategies 5.1 Cultural practices for disease prevention Cultural practices play a crucial role in managing Alternaria leaf spot (ALS) in cotton. Implementing crop rotation and avoiding the cultivation of cotton in consecutive seasons can reduce the inoculum load in the soil. Proper field sanitation, including the removal of plant debris and weeds, can also help minimize the sources of infection. Additionally, optimizing planting density and ensuring adequate spacing between plants can improve air circulation, thereby reducing the humidity levels that favor the growth of Alternaria spp. (Venkatesh et al., 2016; Al-lami et al., 2022). 5.2 Chemical and biological control measures Chemical control measures involve the application of fungicides to manage ALS. Fungicides such as prochloraz have been found to be effective against Alternaria spp., including A. alternata and A. koreana, which are known to cause leaf spot in various crops (Figure 2) (Wang et al., 2023). Regular monitoring and timely application of fungicides can help in controlling the disease. However, reliance solely on chemical control is not advisable due to the potential for resistance development and environmental concerns. Biological control measures, although less commonly used, can also be effective. The use of biocontrol agents such as Trichoderma spp. and Bacillus spp. can suppress the growth of Alternaria spp. by competing for nutrients and space, as well as through the production of antifungal compounds. Integrating biological control with chemical treatments can provide a more sustainable approach to managing ALS. Figure 2 Pathogenicity of fungal isolates (Photo credit: Wang et al., 2023) Imagine caption: (A) Signs on leaves of controls treated with PDA after 4 days. (B-D) Signs on leaves inoculated with mycelium blocks of A. alternata (isolates 11, 13) and A. koreana (isolate 12) after 4 days. (E) Signs on leaves of controls treated with sterile water after 5 days. (F–H) Signs on leaves of controls handled with sterile water after 5 days. Signs on leaves inoculated with 10 µL of conidial suspension (106 conidia/mL) of A. alternata (isolates 11, 13) and A. koreana (isolate 12) after 5 days (Adopted from Wang et al., 2023) 5.3 Resistant varieties and breeding programs Breeding for disease-resistant varieties is a long-term and sustainable strategy for managing ALS in cotton. Research has shown significant genotypic variations in resistance to ALS among different cotton genotypes. For instance, certain upland cotton lines, such as glandless NuMex COT 15 GLS, NM 13P1117, and NM 12Y1002, have demonstrated consistent resistance to ALS in multiple trials (Fan et al., 2023). Similarly, some commercial transgenic varieties like FM 2484 B2F, PHY 444 WRF, and NG 4545 B2XF have also shown resistance.
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