Water for agriculture is critical for future global food security, because agriculture constitutes the largest user of fresh water, with irrigation withdrawals representing approximately 70% of total water use (Knox et al., 2012). However, only half of this, is estimated to reach the intended crop, the rest being lost somewhere between the point of extraction and the crop (Turral et al., 2010). The significant quantity of water used by agriculture for production raises the question as to whether agriculture could become more efficient in its water use (Hatfield, 2015), on the fact that most fresh water is stored as glaciers or deep groundwater (Oki & Kanae, 2006). Furthermore, global warming threatens to exacerbate the situation with a predicted reduction in water resources. In the Yucatan Peninsula, an increase in the drought severity index is expected (Orellana et al., 2009), which could have a direct effect on crops. Habanero pepper (Capsicum chinense Jacq.) is the most important crop in the Yucatan Peninsula. As the hottest pepper, it represents one of the major spices traded on international markets due to its typical burning sensation, known as pungency, caused by the presence of capsaicinoids (Garruña-Hernández et al., 2013). However, few studies of water use are available on this species. Quintal-Ortiz et al. (2012), applied five irrigation levels in pots with drainage and concluded that an irrigation level (IL) of 60% of available water capacity (AWC) of substrate increased both plant growth and fruit size. It is not clear in that study, was all the water used in evapotranspiration? What would happen when using pots without drainage? Movement of water throughout soil profile is known to occur when the amount of water exceeds the soil storage capacity and water moves downward under gravitational force. Respectively, in the search for a better water use efficiency, the aim of this research was to identify the best irrigation level for Habanero pepper plants based on AWC of substrate.

The irrigation level (IL) affected early plant growth, the IL of 60% could not be evaluated because pots became flooded and plants did not survive. A previous study on IL in C. chinense (Quintal-Ortiz et al., 2012) concluded that 60% of AWC increased both plant growth and fruit size, but pots used for this study had drainage.

Irrigation treatments affected significantly plant growth (plant height, stem diameter, leaf area and dry matter). However, plant genotype did not have a significantly effect on plant growth parameters. Accordingly to González-Dugo et al. (2007), the pepper growth is closely linked to the water amount applied. Our results showed plant height of the jaguar genotype irrigated at 40%, was statistically similar to H241 (92±3.7 and 79±4.8 cm respectively) genotypes, but different to other treatments. Decreasing the IL from 40 to 20% produced a negative effect on plant height in both Jaguar and H241 genotypers (Figure 2A). The same occurred for stem diameter in all genotypes (Figure 2B). Similar responses were observed by Achten et al. (2010), who applied dry treatments to Jatropha curcas and showed there was a decrease in both stem length and diameter. In addition, dry matter was higher in the roots. However, in our study, there was a higher root dry weight in plants with high irrigation levels (Table 1). All genotypes had similar leaf area at an IL of 20%, but at an IL of 40%, leaf area of genotypes H225, H241 and H244 had at least 48% greater leaf area than Jaguar plants (Table 1). Similarly, there were no significantly differences in total dry matter among genotypes from an IL of 20%, but with an IL of 40% the total dry weight of H241 and Jaguar plants was 30 and 28% greater than plants of H226. Clearly, an increase in dry matter was produced by raising the IL (Table 1), such as occurs in tomatoes, where total dry matter accumulation is significantly depressed by soil water deficit (Patanè et al., 2011).

Figure 2

In all genotypes, the inflorescence stage was earlier in plants with an IL of 20%, compared to an IL of 40% (Figure 3). This was a stress consequence due to water deficit. The degree of crop sensitivity to water deficit during the different developmental stages of a plant species is a significant characteristic to consider (Jaimez et al., 2000). Morales et al. (2013), found that raspberry under drought stress showed earlier inflorescence, while Ávila et al. (2012), observed that flowering was increased by water stress in Citrus. However, Jaimez et al. (2000), observed that low water availability delays the occurrence of maximum flowering in C. chinense. Our results showed the earlier inflorescence time was in response to water stress, H241, H244 and H226 genotypes, showed only two days of delay in flowering development under both irrigation treatments (Figure 3). Inflorescence time could be influenced by genotype.

Figure 3

The soil water potential (Ψs) decreased from morning to afternoon, but it was lower in IL of 20% both at 8:00 (Figure 4A) and 14:00 h (Figure 4B). Therefore, water stress conditions were evident in the most restrictive treatment (IL of 20%).

Figure 4

Regarding the chlorophyll (Chl) fluorescence parameters, the values of F_v/F_m reflect the potential quantum efficiency of PSII and are performed as a sensitive indicator of plant photosynthetic performance (Maxwell & Johnson, 2000). With the exception of genotype H225, F_v/F_m in leaves was higher in plants in an IL of 40% than in an IL of 20%. Plant leaves of H241 (0.81), H244 (0.83) and H226 (0.83) had higher F_v/F_m values. An F_v/F_m value of around 0.83 is an optimal measurement for most plant species (Maxwell & Johnson, 2000). Likewise, H244, H226 and H241 plants at an IL of 40% exhibited better performance both in terms of electron transport rate (ETR) and effective photochemical quantum yield of photosystem II (Φ_PSII). Genotypes H225 and Jaguar therefore showed greater physiological susceptibility to the lack of water. Penella et al. (2014), did not find any differences among control and water stress treatments in the F_v/F_m of 18 pepper genotypes. However, Ogaya & Peñuelas (2003), showed drought treatment produced a decrease in F_v/F_m values of Quercus ilex and Parentucellia latifolia plants.

Figure 5

Figure 6

Moreover, drought treatment also produced a slight decrease in ETR values for both species, and the highest PSII Yield was in the season when no drought stress occurred (Ogaya & Peñuela, 2003). The effects of abiotic and biotic stresses on plant photosynthetic performance lead to fitness and yield decreases. The maximum quantum efficiency of photosystem II (F_v/F_m) is a parameter of Chl fluorescence classically used to track changes in photosynthetic performance (Bresson et al., 2015). If Chl fluorescence parameters can provide useful tests of photosynthetic performance in vivo and indicate the extent to which performance is limited by photochemical and non-photochemical processes (Baker, 2008), H241, H244 and H226 plants at an IL of 40% can be considered to show excellent photosynthetic performance, avoiding damage by photo inhibition.

The IL of 20% decreased the soil water potential (Ψs) sufficiently to cause water stress in plants and H241 and Jaguar plants showed good performance on growth parameters at an IL of 40%. However, inflorescence time was earlier in H241, H244 and H226 plants. In addition, Chl fluorescence measurements confirmed that genotypes H241, H244 and H226 had higher physiological performance than Jaguar; i.e. they are less probably due to photo inhibition damage. Meanwhile, the IL of 60% caused flooding and plant death without drainage. These results suggest the enforcement of a suitable irrigation level based in available water capacity of substrate (40% in this research) coupled with a vigorous genotype can encourage healthy plants and high water use efficiency.