**3. Seed technology**

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

**45**

infection [23, 24].

*Hot Water Seed Treatment: A Review*

**4. Hot water treatment**

germination rate of cabbage seed.

*DOI: http://dx.doi.org/10.5772/intechopen.91314*

under optimum environmental conditions [8–10]. Extensive seed germination and seedling appearance has increased the occurrence of pre-damping off mortality caused by soil-borne fungi [11]. This also leads to establishment of weeds in the fields even before the crop seedlings are mature enough to be cultivated, competing with the main crop for nutrients, and moreover, they hinder the processes of

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

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

**5. Effect of hot water treatment on different vegetables**

Nega et al. [15] stated that even with longer treatment times, hot water treatment with a temperature of 40°C had no significant effect on the seed-borne pathogens. However, on all the crops investigated, hot water treatments at temperatures

fertilisation, chemical application and mechanical harvesting.

under optimum environmental conditions [8–10]. Extensive seed germination and seedling appearance has increased the occurrence of pre-damping off mortality caused by soil-borne fungi [11]. This also leads to establishment of weeds in the fields even before the crop seedlings are mature enough to be cultivated, competing with the main crop for nutrients, and moreover, they hinder the processes of fertilisation, chemical application and mechanical harvesting.
