Screening of different wheat genotypes against leaf rust and role of environmental factors affecting disease development

1 Introduction

Mostly population of the earth is a farming community. The importance of agriculture on the earth is undeniable as it is the backbone of the any agriculture country . It contributes 25 percent of the total GDP of our country . It consumes 48% of the labor force and 70% population is related to agriculture directly or indirectly. It plays an important role in foreign exchange and stimulates growth in other sectors. (Importance of Agriculture in country ’s economy and development). Wheat is the staple food of the mostly population of our country and 40% of world food is related to wheat directly or indirectly (Anonymous, 2007). Production of wheat in this country is not so high as compared to other developed countries (Brian, 2006). The reason is that they use good quality seed and technology to get handsome per hectare yield. According to FAO cereal supply and demand, production of wheat was 1,37,443 Million tons in EU-27 listed at No.1. Then, in China having production of wheat 1,21,000 Million tones after that in India 92,000 Million tones, 56,613 million tonnes in the USA, 54,000 million tonnes in Russia, Canada 29,000 million tones and in Australia 24,500 million tones. In this country , its production was 24,330 million tonnes. So, it is a need of an hour to use modern techniques and tools to get a high yield. Now, the government has shown its interest to develop varieties and research on different crops.Fig. 1.Table 1.Table 2.Table 3..

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Fig. 1

The above graph showing the relationship of leaf rust severity with average Temperature and Humidity of 2020–21, 2019–20, 2018–19.

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Leaf rust caused by pathogen Puccinia has more potential to threaten the yield of wheat up to 10% as compared to the other two types of rust stem and yellow rust. The severity of the disease depends upon the developmental stage of the plant and susceptibility of the plant (Duplessis, et al., 2021). The variability of wheat growing conditions favorable climatic patterns, and genomic polyploidy nature it becomes the most financial and nutritional crop (Dubcovsky and Dvorak, 2007). The FAO report on annual global supply and demand for wheat is ample for wheat production (FAO). The population development rate is increasing, which is estimated at 9 billion by 2025 (Chartres and Noble, 2015). To meet the demand for staple food the production of wheat is an important interest for its significance turn out (Schnurbusch, 2019).

The favourable condition for rust to infect the plant at high relative humidity with a temperature range in 15-22°C with optimum temperature for spore’s development is 20C in only 6–8 h for the development of disease. Leaf rust infections can cause yield losses beyond 50 per cent at even earlier stages. The damage to rust in leaves sometimes is less spectacular than that produced by strip (yellow), but as leaf rust frequently occurs the total yearly losses worldwide are likely more than the others. (Huerta-Espino et al., 2011).

Rust challenges the yield of the wheat crop so chemicals are used in terms to prevent and treat the disease incidence, but the chemical nature of the synthetic fungicide has a worse effect on the health metabolic life of humans and animals. It also makes wheat single-quality varieties resistant to the pathogen (Collard and Mackill, 2008). Some measures are proving very helpful to overcome the losses caused by Leaf rust fallowed by researchers as well as field workers including cultivars susceptibility, varieties genetic resistance, climatic interaction, microorganism disease transmission capacity, and field management process (Temesgen, 2015). Some plants have pathogens-toxic substances that are isolated from plants and administered to diseased plants.

During 2017–18, wheat was cultivated at 8734 thousand hectares than that of 8982 thousand hectares in the previous year which is decreased by 2.6 percent. Its production was 25.492 million tonnes than previous year production 26.674 million tones and production is reduced to 4.4 percent. The share of wheat cultivation in Pakistan out of total crops is 10.1% and it contributes to 2.2% of the total GDP of the country.

Due to the increase in the population of Pakistan, the requirement for food is increasing day by day. Overall edible consumption in Pakistan, the wheat share is 9%. In farming areas, it is the only single item used than that of urban places. The country’s population is growing at the rate of 2.4 percent annum. Therefore, the demand of wheat also increased in the future. According to projected data, in 2025, the requirement of wheat will be 31.415 million tonnes and the area of cultivation will be 9.050 million/hectare. In 2030, its demand would increase up to 34.25 million tones having the same area under cultivation (wheat in Pakistan, A status paper by PARC, 2013).

Wheat is grown as a rabi crop in the spring season in Punjab, Sindh, NWFP, and in northern areas of Balochistan. It is grown in the winter season in limited areas as well. In Punjab, wheat is grown in irrigated areas while its cultivation in rainfed areas is 10%, depending only on rainwater for its growth. The wheat cultivated area in Punjab is 6.026,500. In Sindh, most of the land is irrigated and the area of cultivation is 1,103,600. (M.S.Cheema and M.Hussain vol. 45 Annual wheat newsletter).

Diseases include rust (leaf, stripe, stem) smut, karnal bunt and powdery mildew caused economic losses to wheat crops (Soliman, N et al.,2012). Puccinia triticina has been an issue for the wheat crop that causes yield losses over large areas (Kolmer JA 2005). It is an airborne disease caused by Puccinia triticina. Spores of this fungus travels thousands of miles and effected different continents. Pakistan is facing a lack of appropriate varieties for yield and to tackle disease (Hussain et al., 2006).

In western Australia loss of 20 million dollars caused by leaf rust was reported. In Pakistan, it causes 10 % yield losses in 1978 (Hassan 1979). In 1978, an epidemic of leaf rust resulted in losses of 86 US dollars (Hussain et al., 1980). At a severe level, it can cause fifty percent yield losses. (Ahmad et al. 2010).So, it is a need of an hour to develop resistant varieties every year because it is a potential threat to any variety that its resistance could be broken. So, varieties are screened against leaf rust to evaluate its potential.

2 Materials and method:

3 Results and discussion

Genotypic resistance is the most appropriate and environment friendly way which is economical to control losses, caused by leaf rust. That’s why these experiments were conducted to find out where the resistance of different varieties was tested against leaf rust to find out the best varieties in Pakistan that can perform better against leaf rust. The response showed by the entire crop is divided into 8 categories to critically observe the effect of the disease.

Screening of wheat varieties in 2018–19, 2019–20 and 2020–21 showed different results against leaf rust. Out of 45 varieties, three varieties were resistant showing the same response in three years. Only one variety (Pakistan-81) was susceptible throughout this period. While other varieties showed a mixed response.

Temperature plays an important role in the development of disease and sporulation. The development of leaf rust depends upon temperature, humidity, wind speed and rainfall of the field area as the landing of urediniospores disease incidence and disease severity is much concerned by these environmental factors. The temperature has a negative correlation with the disease while humidity, rainfall, and wind speed have a positive correlation with disease development. Before March, despite low temperature, humidity and wind speed was not favorable for disease development. During the first week of March, environmental conditions were favorable for disease development as the temperature was low and humidity and wind speed were high causing urediniospores to infect, multiply and spread at a higher rate. Therefore, brown rust spores were observed in Morocco on March 4 followed by Sahar-06.

Therefore, we compare three years of data having Average Temperature and Humidity from Mid- January to Mid-April to find out the environmental conditions that favor the infection of urediniospores.

4 Conclusion

Only three varieties were common that showed resistance after comparing the data of 2018–19, 2019–20 and 2020–21. Varieties named Johar-16, A1-180015, A2-180026 were resistant against leaf rust after infection of urediniospores that were artificially inoculated. While Pakistan-81 was only one variety that was susceptible throughout this period.

Varieties were cultivated in early October for screening against leaf rust in Pakistan. Due to this, plants reached their dough and maturity stage early when urediniospores infect different varieties. That’s why losses caused by urediniospores infection were reduced. The flowering stage is most vulnerable causing a high yield loss when urediniospores cause infection. But, environmental factors also play an important role in disease development. It is concluded that temperature, humidity and rainfall increase chances of leaf rust infection after comparing three years of data. The temperature has a negative correlation with leaf rust while humidity and rainfall have a positive correlation with leaf rust. Spores need a low temperature between 18 and 25⁰C humidity above 80% and rainfall in the range of 10 mm favors disease a lot. Urediniospores require six to eight hours of moisture for infection (Dawn, 2008). Wind speed is also needed for spreading urediniospores to long distances as they can travel and infect on the continental level.

So, by cultivating and crossing above mentioned varieties we can minimize our annual yield loss. To protect wheat from leaf rust it should be cultivated from 15Oct-30 Oct as infection of urediniospores in Pakistan usually occurs in Mid-February to March and at this stage, the plant would have a dough or maturity stage. At this stage, the effect of leaf rust on grain yield is minimized. After the flowering stage, the plant concentrate on its grains and our main purpose is a grain, not fodder. So, chemical application after infection of leaf rust is a foolish activity because grains are consumed by humans which are hazardous for their life. Therefore, after infection of leaf rust after flowering stage, no chemical nor water and fertilizer should be applied as the main purpose of urediniospores is to turn leaves yellow which ultimately die the entire leaves which is a good sign ultimately for plant grain.