**4. Hot water treatment**

Capsicum

is of no exception.

**2. Disease of sweet pepper**

bell pepper is grown in summer, whereas in the states of Karnataka, Tamil Nadu, Bihar and Maharashtra, it is grown in the autumn season [4]. In India, bell pepper covers an area of 29,800 ha with 171,370 tonnes production and productivity of 5.75 tonnes/ha [5]. Sweet pepper is a warm-season crop, which grows well under an extended frost-free season, with the capability of producing high yields of exceptional quality. The best temperature range for sweet pepper growth is 20–25°C, whereas the best germination temperature is 29°C. A temperature of less than 29°C reduces the growth of seedling, leading to increased exposure of seedlings to insects, diseases or salts, resulting in damaged or dead seedlings [6]. High temperatures adversely affect the productivity of many plant species of which sweet pepper

High humidity in the environment and moist soil together with optimum temperature result in high incidence of various diseases. Diseases like bacterial spot (*Xanthomonas campestris* pv*. vesicatoria*), *Cercospora* leaf spot (*C. capsici*), anthracnose (*Colletotrichum capsici*) and virus diseases are seed borne in nature. To avoid the occurrence of such diseases, seed treatment with various chemicals has been recommended from time to time [7]. But in present day agriculture, use of chemicals for crop production is discouraged. Hence, other alternative treatments for disease control must be developed. One such treatment is with hot water which is economically as well as temporally feasible. Farmers, along with a little technical assistance, can easily adopt this treatment. This treatment is also successful for destroying viruses like *mosaic virus* that affect bell pepper. It is very efficient in destroying pathogens borne both outside the testa and inside the seed testa. In this

area no such work has been done in the case of bell pepper.

Bacterial spot (*Xanthomonas campestris* pv. *vesicatoria*), bacterial wilt (*Pseudomonas solanacearum*), anthracnose/ripe fruit (*Colletotrichum* spp.), *Cercospora* leaf spot/frog eye leaf spot (*C. capsici*), bacterial canker (*Clavibacter michiganensis*) and viruses like Tomato spotted wilt virus (TSWV) are some of the most important diseases of sweet pepper that cause huge economic losses to the farmers. Seed-borne diseases of bell pepper are the most important problems in organic farming systems because of the limitation in chemical control methods. For the successful management of any disease under normal conditions, sanitation, elimination of primary source and chemical protection at initial stages are some of the measures recommended. Various workers are now engaged in developing and testing the non-chemical methods for seed-borne diseases of vegetables including

Seed is the primary and essential starting point of a wide range of horticultural crops, including the majority of vegetables. The high-quality seeds of vegetable varieties that display early, consistent, dynamic seedlings and better- and goodquality fruits from individual seed sown at favourable or unfavourable conditions have increased significantly in recent years. Seedling emergence and field stand establishment is one of the problems faced by the growers, especially in early planting where adverse conditions are prevailing (low temperature and high soil moisture). Delayed, erratic germination and emergence, poor stand, slow early seedling growth rate and non-uniform maturity often limit crop production even

**44**

bell pepper.

**3. Seed technology**

The most appropriate seed treatment with respect to least damage, economy, efficiency and application is hot water soaking. It is an old-age practice based on treatment with hot water whose temperature is high enough to kill the pathogen but not high enough to harm the seed, hence a very good technique to control many seed-borne diseases [12, 13]. Heat treatment may be applied for agricultural commodities by (1) immersion in hot water, (2) exposure to vapour heat, (3) exposure to hot dry air, (4) treatment with infrared radiation or (5) microwave radiation. Hot water treatments of seed and plant material are classical thermophysical methods of plant protection and are more eco-friendly and effective than chemical treatments.

Hot water treatment can be damaging or not practical for seeds of peas, beans, cucumbers, lettuce, sweet corn, beets and some other crops [12, 14, 15], but it is highly recommended for pepper, eggplant, tomato, cucumber, carrot, spinach, lettuce, celery, cabbage, turnip, radish and other crucifers. It may also severely damage old seeds, and therefore, a small sample of any seed lot over 1 year should be first treated and then tested for germination to determine the amount of injury that may occur. Hot water treatment is recommended for seeds with surface or deep-seated infections. Effective treatment temperature and duration have to be found out for every vegetable crop and the relevant pathogens. The principle is to eliminate the pathogens as far as possible without decreasing germination of seeds. For example, just a 5-min difference in treatment time can lead to diverse differences in the germination rate of cabbage seed.

A number of tests and studies of heat treatment must be undertaken to optimise the time and temperature that are most adaptable to the seeds to be treated and the pathogens to be killed before practical application. Susceptibility to heat damage may differ among different varieties of plant species [16, 17]. The time/temperature combination for a given plant seed depends on many factors interacting with the heat susceptibility of the host, viz., conditions of external layers, dormancy, moisture content, age and vigour [18]. Particularly, it has long been known that the smaller the initial water content of seeds is at the time of heating, the greater the resistance to high temperatures [19]. Two major groups of proteins may be activated by the hot water treatments that induce fruit resistance: heat shock proteins (HSPs) and pathogenesis-related (PR) proteins. HSPs are believed to play a major role in thermotolerance [20–22]. Among the PR proteins, most characterised enzymes chitinases and β-1,3-glucanases hydrolyse polymers of fungal cell walls and are, therefore, thought to be involved in the plant defence mechanism against fungal infection [23, 24].
