**2. What is drought resistance?**

The ability of a plant to maintain favorable water balance in its tissues (turgidity/turgor) when exposed to drought stress is a manifestation of drought resistance. Turgidity refers to the condition of the leaf when it is wide open and fully facing the sky. When a leaf loses turgor it rolls (in crops like rice) wilts (in crops like legumes) and ultimately dries up. Loss of turgor is an indication that the transpiration demand is more than the water being supplied from the soil through the plant. Sometimes, the loss of turgor can be a temporary phase during high temperatures prevalent during midday.

Maintenance of turgor under low-moisture conditions is crucial. It implies continued transpi‐ ration. This requires the stomata to be open thus facilitating gas exchange, a prerequisite for photosynthesis. The transpiration pull thus generated provides the suction force (one of the requirements) for water uptake by roots. This also keeps the leaf cool and prevents drying and subsequent dying. Thus, a favorable water balance under drought condition is a key to a plant's survival and productivity.

While continued transpiration has many advantages to the plant/crop survival, the final and economically useful manifestation of drought resistance is the magnitude of grain yield that is obtained at the end of the season, when the crop has been challenged by drought. Maintenance of turgor, transpiration, biomass or greenness is of little use to the farmer who wishes grain yield. While maintenance of turgor and survival under stress are of academic interest, grain yield is of practical value. Thus, ultimately, in grain crops the grain yield is the manifestation of drought resistance. Even under non-stress condi‐ tions, it is the grain yield (or the economic product in non-grain crops) that is a measure of a plants' performance [7]. Any trait that contributes to this would be a useful selec‐ tion criteria in a breeding program.

Daek blue – countries with plentiful water (>1,700 m3/person/day) Medium blue – countries with water stress (<1,700 m3/person/day) Light blue countries with water scarcity (<1,000 m3/person/day)

2006. P 37 [2]"

in the traditional manner".

152 Plant Breeding from Laboratories to Fields

**2. What is drought resistance?**

temperatures prevalent during midday.

**Figure 1.** Water scarcity map of the most vulnerable parts of the world. Left 2005, Right 2015. Borrowed from "Blue revolution initiative Strategic framework for Asia and the Near East, Bureau for Asia and the Near East, USAID, May

Breeding for drought tolerance in any given crop, has immense value to the farmers as their livelihood depends on the harvest(s). It bears a positive effect on the farmers' economic health, family well-being and harmony in the society. It affects poor farmers more than the rich ones. Complete or partial loss of harvest in drought years is known to trigger panic reaction, migration and decrease or extinction of flora and fauna of the particular habitat. There have been scores of farmer suicides due to losses caused by drought and associated problems in different States of India [3, 4]. A link between drought and suicides has been established in Australia [5], Africa, and in the South America. Thus as a trait, drought resistance has immense value to the individual farmer and the society. According to [6] the "future imperative is clear —Asia cannot continue to depend on the quantity and quality of freshwater for rice cultivation

The ability of a plant to maintain favorable water balance in its tissues (turgidity/turgor) when exposed to drought stress is a manifestation of drought resistance. Turgidity refers to the condition of the leaf when it is wide open and fully facing the sky. When a leaf loses turgor it rolls (in crops like rice) wilts (in crops like legumes) and ultimately dries up. Loss of turgor is an indication that the transpiration demand is more than the water being supplied from the soil through the plant. Sometimes, the loss of turgor can be a temporary phase during high

Maintenance of turgor under low-moisture conditions is crucial. It implies continued transpi‐ ration. This requires the stomata to be open thus facilitating gas exchange, a prerequisite for The pattern of responses that a plant choses to trigger has been collectively referred to as drought resistance. Further classifications of responses fall into three categories namely, drought escape, dehydration avoidance and dehydration tolerance [8]. Dehydration avoidance is a reaction when the plant maintains a high level of water status or turgor under conditions of increasing soil-moisture deficit. Finally, drought resistance is referred to as a plants' ability to sustain the least injury to life functions at decreasing levels of tissue water status or turgor. Drought escape refers to the ability of the plant to com‐ plete its lifecycle before the onset of drought or adjust its phenology so that the crucial developmental stages escape the adverse impacts of drought [9]. Delayed flowering, is one such phenological adjustment.

Broadly, plants adopt two strategies, which involve reducing their water expenditure called "water savers" or "pessimistic plants" or accelerating water uptake sufficiently so as to replenish the lost water called as "water spenders" or "optimistic plants". A plant can maintain turgor by adopting one or both of the following strategies depending on genotype and environmental factors.


The drought resistant variety or hybrid that is developed is also expected to possess the ability to contend with excess moisture. Many times low-moisture and excess moisture can also cause stress to the crop within the particular season. The variety or hybrid must also possess certain degree of resistance to common diseases or pests that are prevalent in the area that is targeted.
