7. Types of irrigation in tomato cultivation

#### 7.1. Sprinkler irrigation

These systems include center pivot, linear move, traveling gun, permanent set, and portable aluminum pipe with sprinklers that supply the irrigation water in sprays to the crops. The idea is to mimic the natural rain drops. Sprinkler systems used in tomato production are normally adjusted to deliver at least an inch of water every 4 days. The system is also designed to supply the water in such a way that runoff is prevented [41]. The type of soil is also considered in adjusting the speed of the sprinkler irrigation system. Whereas faster speed (3 inches per hour) is preferred in sandy soils, slower speed is preferred in loamy soils (1 inch per hour). High level of application uniformity is essential every plant is covered to ensure uniform growth and development throughout the field [42].

#### 7.2. Drip irrigation

Drip irrigation has become the standard practice for tomato production. Although it can be used with or without plastic mulch, its use is highly recommended with plastic mulch culture. One of the major advantages of drip irrigation is its water use efficiency. When used in conjunction with plastic mulch, the tubing can be installed at the same time the plastic mulch is laid. In drip irrigation system, water is delivered to each plant usually done with tubes and emitters that carry water from main lines to the base of each plant. In some cases, fertilizer is included in the irrigation water in a system appropriately called "fertigation" [41, 46]. The important thing to note is that water is supplied in such a way that the plants do not wilt. Studies have also shown significant yield increases with drip irrigation and plastic mulch when compared with sprinkler-irrigated tomatoes. The most dramatic yields have been attained by using drip irrigation and plastic mulch, and supplementing nutrients by injecting fertilizers into the drip system. This observation is due to judicious utilization of the water and nutrient resources that are supplied to each plant which is not the case with sprinkler irrigation system. The incidences of weeds also less of a problem, since only the rows are watered and the middles remain dry. Another advantage of drip irrigation is obtained when used in within a high tunnel which is equipped with the ability to inject water-soluble nutrients through the drip lines as the plant needs them.

### 8. Genotype × environment interaction

tomato plant particularly at transplanting, flowering, and fruit development. Adequate supply of water is very essential for attaining the full potential of tomato plants under cultivation [31, 32]. However, agricultural activities in most parts of the tropics are mostly rainfed resulting in short supply of water for farming activities during the dry season. Rainfall amounts are often erratic even during the main growing season resulting in poor crop performance especially in areas where tomatoes are grown in soils with low water holding capacity. The use of irrigation schemes provides the needed water required for crop production. This makes supplemental irrigation essential for commercial tomato production to sustain consistent yields of highquality tomatoes during the off-season to meet demand of consumers. Studies have shown that irrigation increases annual tomato yields by an average of at least 60% over dryland production [32, 33]. The quality of tomatoes cultivated under irrigation has also been found

These systems include center pivot, linear move, traveling gun, permanent set, and portable aluminum pipe with sprinklers that supply the irrigation water in sprays to the crops. The idea is to mimic the natural rain drops. Sprinkler systems used in tomato production are normally adjusted to deliver at least an inch of water every 4 days. The system is also designed to supply the water in such a way that runoff is prevented [41]. The type of soil is also considered in adjusting the speed of the sprinkler irrigation system. Whereas faster speed (3 inches per hour) is preferred in sandy soils, slower speed is preferred in loamy soils (1 inch per hour). High level of application uniformity is essential every plant is covered to ensure uniform growth and

Drip irrigation has become the standard practice for tomato production. Although it can be used with or without plastic mulch, its use is highly recommended with plastic mulch culture. One of the major advantages of drip irrigation is its water use efficiency. When used in conjunction with plastic mulch, the tubing can be installed at the same time the plastic mulch is laid. In drip irrigation system, water is delivered to each plant usually done with tubes and emitters that carry water from main lines to the base of each plant. In some cases, fertilizer is included in the irrigation water in a system appropriately called "fertigation" [41, 46]. The important thing to note is that water is supplied in such a way that the plants do not wilt. Studies have also shown significant yield increases with drip irrigation and plastic mulch when compared with sprinkler-irrigated tomatoes. The most dramatic yields have been attained by using drip irrigation and plastic mulch, and supplementing nutrients by injecting fertilizers into the drip system. This observation is due to judicious utilization of the water and nutrient resources that are supplied to each plant which is not the case with sprinkler irrigation system. The incidences of weeds also less of a problem, since only the rows are watered and

to be better than nonirrigated fields [20].

78 Recent Advances in Tomato Breeding and Production

development throughout the field [42].

7.1. Sprinkler irrigation

7.2. Drip irrigation

7. Types of irrigation in tomato cultivation

Multilocation trials are usually performed by researchers to evaluate new or improved genotypes across multiple environments (locations and years), before they are promoted for release and commercialization. This is systematic approach undertaken to increase yield stability of new crop varieties in stress-prone environments [47]. Data generated from such trials are important for (i) accurate estimation and prediction of yield based on limited experimental data; (ii) determining yield stability and the pattern of genotypes response across environments; and (iii) providing reliable guidance for selecting the best genotypes or agronomic treatments for planting in future years and at new areas [48]. However, the performances or ranking of the genotypes in such experiments are usually not the same in the different environments. This is because of interactions between the genotypes and the environments [49, 50]. This type of interaction is known as genotype × environment interaction (GEI), and may complicate the selection and recommendation of genotypes evaluated in diverse environments [51, 52]. The importance of GEI in genotype evaluation and breeding programs has been demonstrated in almost all major crops [53–57]. The GEI reduces the association between the phenotypic and genotypic values and leads to bias in the estimation of gene effects and combining ability for various characters that are sensitive to environmental fluctuations less reliable for selection [57].

Genotype × environment interactions can be classified into three broad types (Figure 3) (i) "no" GEI, (ii) non-crossover interaction, and (iii) crossover interaction [58]. The number of environments (E) and the number of genotypes (G) determine the number of GEI possible and that, the higher the number of environments and genotypes the greater the number of possible G × E interactions. Thus, with two genotypes and two environments, and with only a single criterion, at least four different types of interactions are possible. With 10 genotypes and 10 environments, 400 types of interactions are possible, which would undoubtedly make their implications and interpretation more difficult to comprehend [59, 60].

#### 9. No G × E interaction

When there is no GEI, the effects of each of the risk factors are similar across the levels of the other risk factors. A "no" GEI occurs when one genotype (G1) constantly performs better than the other genotype (G2) by approximately the same amount across both environments. Figure 3A, B shows that G1 and G2 perform similarly in two environments, because their responses are parallel and stable. The variations in trait expression across a range of environments for the two genotypes are therefore additive. Moreover, the intergenotypic variance

intergenotypic variance remains unchanged. Figure 3E is also a representative of a crossover interaction as the genotypes change ranks between the two environments. There is also a change in magnitude of intergenotypic variance. Moreover, the difference between genotypes G1 and G2 in environment E1 is smaller than that in E2, and the direction of environmental modification of the two genotypes is the same. The illustration in Figure 3F is a crossover

Genotype × Environment Interaction: A Prerequisite for Tomato Variety Development

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Multilocation trials are conducted to evaluate yield stability performance of genetic materials under varying environmental conditions [55]. The relative performance of genotypes for quantitative characteristics, such as yield and other characteristics, influences yield to vary from an environment to another. To develop a genotype with high yielding ability and consistent performance, high attention should be given to the importance of stable performance for the genotypes under different environments and their interactions. This enables the breeding of better crop varieties that have buffered and can give stable and consistent performance across different environments and seasons [59]. To attain this, feat genotypes are evaluated in multienvironment trials (METs) by testing their performance across environments and selecting the best genotypes in specific environments. The main objective is to eliminate genotype by environment interaction results from differences in the sensitivities of genotypes to the conditions in the target environment [62]. This leads to inconsistent performances of genotypes across environments and limits the efficiency of selection of superior genotypes [56].

13. Tools/methods for genotype × environment interaction analysis

Analysis of GEI is important to obtain information on the performance of genotypes in terms of adaptability and stability. Analysis of variance is performed across environments in order to identify the presence of GEI in multilocation trials. When the GEI variance is found to be significant, then one of the various methods for measuring the stability of genotypes can be used to identify the most stable genotype(s). Several statistical methods have been proposed for analysis and interpretation of GEI [63–66]. The joint regression analysis [67–69] method has been widely used; nonetheless, several limitations of the method have been stated [70, 71]. For example, see [48]. The PCA method has the ability to overcome the limitations associated with the linear regression method by giving more than one statistic, that is, the scores on the principal component axes, to describe the response of a genotype. Another method which has been proposed for analysis of GEI is the cluster analysis which is a numerical classification technique that defines groups of clusters of individuals [48, 72]. Currently, the additive main effects and multiplicative interaction (AMMI) model [64, 71] and genotype main effect plus genotype × environment interaction (GGE) biplot methodology [66] are the two most powerful statistical tools used by many researchers for the analysis of multilocational trial data. The AMMI model combines the analysis of variance for the genotype and environment main

interaction with the environmental modification in opposite direction [58].

12. Multilocation trial for tomato production

Figure 3. Graphical representation of the "no" interaction, non-crossover interaction, and crossover interaction types of genotype-environment interactions (Source: [58]).

remains unchanged in the two environments and the direction of environmental modification of genotypes is the same. In Figure 3A, there is a main effect of G, and in Figure 3B, there is a main effect of environment [58].

#### 10. Non-crossover G × E interaction

Figure 3C signifies a non-crossover type of GEI. Unlike in Figures 3A and 3B, the difference in performance is not similar across the environments. The G1 and G2 respond differently to the two environments but their ranks remain unchanged. The response of the two genotypes under different environments is therefore not additive, and the magnitude of intergenotypic difference increases. Moreover, the environmental modifications of the two genotypes are in the same direction [58].

#### 11. Crossover G × E interaction

The different and inconsistent response of genotypes to diverse environments is regarded as crossover GEI, when the ranks of genotypes vary from one environment to another [1]. Crossover interaction suggests that no genotype is superior in multiple environments [61]. Figure 3D illustrates a crossover type of GEI where the direction of environmental modification of genotypes, G1 and G2 is opposite: the performance of G1 increases and that of G2 decreases. The genotypic ranks change between the two environments, but the magnitude of intergenotypic variance remains unchanged. Figure 3E is also a representative of a crossover interaction as the genotypes change ranks between the two environments. There is also a change in magnitude of intergenotypic variance. Moreover, the difference between genotypes G1 and G2 in environment E1 is smaller than that in E2, and the direction of environmental modification of the two genotypes is the same. The illustration in Figure 3F is a crossover interaction with the environmental modification in opposite direction [58].

### 12. Multilocation trial for tomato production

remains unchanged in the two environments and the direction of environmental modification of genotypes is the same. In Figure 3A, there is a main effect of G, and in Figure 3B, there is a

Figure 3. Graphical representation of the "no" interaction, non-crossover interaction, and crossover interaction types of

Figure 3C signifies a non-crossover type of GEI. Unlike in Figures 3A and 3B, the difference in performance is not similar across the environments. The G1 and G2 respond differently to the two environments but their ranks remain unchanged. The response of the two genotypes under different environments is therefore not additive, and the magnitude of intergenotypic difference increases. Moreover, the environmental modifications of the two genotypes are in

The different and inconsistent response of genotypes to diverse environments is regarded as crossover GEI, when the ranks of genotypes vary from one environment to another [1]. Crossover interaction suggests that no genotype is superior in multiple environments [61]. Figure 3D illustrates a crossover type of GEI where the direction of environmental modification of genotypes, G1 and G2 is opposite: the performance of G1 increases and that of G2 decreases. The genotypic ranks change between the two environments, but the magnitude of

main effect of environment [58].

genotype-environment interactions (Source: [58]).

80 Recent Advances in Tomato Breeding and Production

the same direction [58].

10. Non-crossover G × E interaction

11. Crossover G × E interaction

Multilocation trials are conducted to evaluate yield stability performance of genetic materials under varying environmental conditions [55]. The relative performance of genotypes for quantitative characteristics, such as yield and other characteristics, influences yield to vary from an environment to another. To develop a genotype with high yielding ability and consistent performance, high attention should be given to the importance of stable performance for the genotypes under different environments and their interactions. This enables the breeding of better crop varieties that have buffered and can give stable and consistent performance across different environments and seasons [59]. To attain this, feat genotypes are evaluated in multienvironment trials (METs) by testing their performance across environments and selecting the best genotypes in specific environments. The main objective is to eliminate genotype by environment interaction results from differences in the sensitivities of genotypes to the conditions in the target environment [62]. This leads to inconsistent performances of genotypes across environments and limits the efficiency of selection of superior genotypes [56].
