**4. Emergence of minor diseases as major diseases due to climate change in Indian subcontinent**

### **4.1 Banded leaf and sheath blight**

Banded leaf and sheath blight (BLSB, **Figure 1**) is now become increasingly severe and economically important disease of maize during last three decades or so. During the past it was reported from Sri Lanka by [27] under the name 'Sclerotial' disease for the first time.

That time it was considered as disease of minor importance till it emerged in an epidemic form in the cooler low hills and foot hills region of Himalayas like in the district of Mandi in Himachal Pradesh. In India, this disease was recorded from Tarai region of Uttar Pradesh, for the first time in 1960 [28]. The optimum temperature for this disease is 28°C and high relative humidity (88–90%) in the first week of infection that favors rapid disease progress. However the disease development and spread becomes slow when relative humidity goes below 70% [29]. Additionally, high crop densities favors disease severity. In changing climate scenario the elevated temperature and CO2 concentration are posing higher threat perception of BLSB and becoming severe and now it is considered as a major disease not only in Indian subcontinent but also in many part of tropical Asia wherever maize is grown in warm and humid conditions.

### **4.2 Polysora rust of maize**

Polysora rust (**Figure 2**) also known as southern rust caused by *Puccinia polysora* is an important disease in tropical areas. It has been noticed in many parts

*The Impact of Climate Change on Changing Pattern of Maize Diseases in Indian Subcontinent... DOI: http://dx.doi.org/10.5772/intechopen.101053*

**Figure 1.** *Banded leaf and sheath blight.*

**Figure 2.** *Polysora rust.*

of the world, and it is observed in recent past from the peninsular India (coastal districts of Andhra Pradesh during winter and in Karnataka and Tamil Nadu during rainy season) on certain maize cultivars in Mysore district recorded in 1991 by [30]. The incidence of *P. polysora* has taken a heavy toll in majority of cultivars grown in Karnataka namely Mysore, Mandya, Hassan, Kolar, part of Coorg, Shimoga and Chitradurga district [31]. Disease is favored by wet/humid weather condition for infection and disease development at 12–27°C [32, 33]. Rain drizzle or even heavy dews allow spread of disease [34]. The maximum cardinal temperature for preceding infection period of *P. polysora* was estimated at 42°C and

for the infection period the value ranges from 27–32°C [35–37]. In future, milder winter in temperate areas will increase diseases. Plant biomass and the concentration of CO2 is positively correlated, however it is regulated by the other factors like availability of water and nutrients, competition between weeds, pest and pathogens. Development of biotrophic fungi such as rust and other foliar diseases on plants, promotes high concentration of carbohydrates in the host tissues. It is therefore assumed that the severity of Polysora rust and common rust will be increased in the pocket areas where is prevalence of elevated CO2.
