Diallel Analysis for Morphological and Biochemical Traits in Tomato Cultivated Under the Influence of Tomato Leaf Curl Virus

Eloquent information about the genetic basis of inheritance is important for any breeding program. Therefore, a diallel study was conducted under the influence of tomato leaf curl virus (TLCV) disease, using the eleven advanced lines of tomato. Firstly, the information regarding percent disease index (PDI) was determined via artificial screening with viruliferous whiteflies. Later, these lines were crossed in half diallel mating design to produce fifty-five one-way hybrids. These hybrids and parental genotypes were evaluated for seven morphological and three biochemical traits under open field conditions. Using the Griffing approach (Method II and Model I) basis of inheritance of traits were determined. Also, a Bayesian model was applied to the total yield descriptor. Correlations data indicated that total yield was not correlated with any other trait. The significant general combining ability (GCA) and specific combining ability (SCA) values indicates exploitable genetic variation. The broad-sense heritability values were larger than narrow-sense heritability, showing that selection will be efficient for the improvement of these traits. Hybrid combinations H23, H42 and H49 can be considered efficient for the selection of multiple traits, including yield. Overall, this study provides a useful information regarding the genetics of important traits of tomato under TLCV infestation.


Introduction 28
Tomato (Solanum lycopersicum L.) is among the most cultivated plants; hence, the 29 efforts of its genetic improvement dates back to last century and are still enduring through 30 traditional breeding and genomics-based approaches [1,2]. Tomatoes are well acclimatized 31 and breed to yield under extreme climatic conditions like drought and frost [3][4][5]. But, 32 insect pest and diseases are still big challenges for the successful production of tomatoes. 33 Worldwide, approximately around 146 viruses belonging to 33 different genera are reported 34 to infect tomato plant [6,7]. Among them, the genus Begomovirus causes huge economic 35 losses to tomato production. Belonging to this genus a DNA virus known as the tomato leaf 36 curl virus (TLCV) is a serious disease of tomato and its incidence, can easily result up to 90 37 percent yield loss to the tomato crop [8,9]. 38 Tomato production especially of autumn season crop in Northern India and summer 39 season crop of Southern India is susceptible to the high incidence of tomato leaf curl virus 40 (TLCV) disease [10]. TLCV is transmitted by whitefly(Bemisia tabaci Genn.) in a 41 circulative and persistent manner [11]. Hitherto, in North India, tomato leaf curl New Delhi 42 virus a strain of TLCV reported from New Delhi region of India has an extensive 43 distribution and also infects several other vegetable crops e.g. Eggplant, Squash and 44 Pepper [12]. As a response to TLCV infection plant leaves shows symptoms like, curling 45 of leaf margins, shrinking and thickening of leaf surface. While the overall plant become 46 stunted in growth, with few and misshaped fruits [11]. Extensive efforts in the form of 47 phenotypic screening has been taken in order to identify resistant genotypes . In this 48 respect, the artificial cage inoculation using viruliferous whiteflies is the most competent 49 and reliable method to carry out the screening for TLCV disease. Although with artificial 50 screening, the plant gives a strong reaction response, than it might give under the field 51 conditions [13,14]. 52 Tomatoes are a important source of nutraceuticals like vitamins (C, K, B6 etc.), 53 phenolic acids, and minerals (folate, manganese etc. includes an overall effect of being inbred (B), an additive component (a), and a measure of 148 parent-specific inbred deviation (b). Also, the "Bab" model was applied using an MCMC 149 Gibbs sampler with five chains, 10,000 iterations, and burn-in of 1000 [35]. 150

Artificial Screening 152
Artificial screening with viruliferous whiteflies provided a dissimilar percent of disease 153 incidence (PDI) values for each genotype (Figure 1). The minimum PDI% was recorded in 154 P4 (29.2%, MR), whereas the maximum was recorded with the P1 (100%, HS) ( Figure 1). 155 All the eleven parental genotypes exhibited the TLCV symptoms after 60 days of artificial 156 inoculation with viruliferous whiteflies. On the TLCV disease scale, two lines showed the 157 mild resistance (MR), in contrast, three were highly susceptible (HS), while the rest were 158 susceptible ( Figure 1). 159 Earlier studies have shown that as compared to a natural field environment screening of 160 genotypes for TLCV, artificial screening is more useful as it ensures a uniform disease 161 infection, and leave few chances for a susceptible plant to escape infection due to non-162 preference and loss of whiteflies infectivity. But, 100% disease incidence is also common 163 with

3.2.Variation in Parents and Hybrids 176
The magnitude of the mean squares of genotypes indicated that there were significant 177 differences among the genotypes for all morphological characters studied pointing out the 178 presence of genetic variability (Table 2). Similarly, significant GCA and SCA effects for all 179 measured traits were detected (P ≤ 0.01). The lowest values of GCA/SCA ratio was noted 180 for polar diameter and TSS content (around 0.05) while the highest was recorded for the 181 fruit weight (0.34). The remaining seven traits ranged from 0.10 to 0.16 (Table 2). This 182 indicated that the non-additive gene effects were more prevalent for the characters under 183 investigation. In general, the GCA variance was higher than that of SCA variance for the 184 characters studied. The broad-sense heritability values were higher (above 0.9) than the 185 narrow-sense heritability(

Bayesian Model-Based Estimates and Predictions of Total Yield 206
Both GCA and SCA contributed for the total yield showing that both additive and 207 nonadditive effects were significant. However, GCA values for the total yield was higher 208 than the SCA values ( Table 2). The predicted means further revealed this with the 209 BayesDiallel Bab model (Figure 2.). 210 The fixed and individual strain additive effects were more stable and less desperessed, 211 than the parent of origin and inbreeding effect (Figure 3).   (Figure 4). Previously, in case of cross-pollinated carrots, it was found that the 226 influence of nonadditive variation was largely due to the overall inbred penalty (non-227 additive effects), which contributed significantly to canopy height, shoot biomass, and root 228 biomass [35]. 229 230 Figure 2. Total yield data of 55 hybrids and 11 parental genotypes in a half diallel. 231 On the left, of parental (P1 to P11), with crossed boxes indicating the missing data 232 (as half diallel was used) and the shaded box representing the values based on the 233 horizontal scale (below). The right side graph shows predictive means based on the 234 Bab diallel model on the scale of (-1.04 to 1.19). 235

GCA and SCA estimates 241
Estimates of general combining ability are presented in Table 4. The estimates were  242 highly significant for all the characters studied for dry matter content. P2 expressed the 243 highest GCA effect (0.346. For equatorial diameter, P4 was the best general combiner with 244 the estimates of 0.273. Regarding fruit weight P5 (9.596) was the best general combiner 245 followed by P8 (8.453) and P7 (7.770) (

258
The results of specific combining ability estimates are given in A total of 14 correlations were found to be significant (P < 0.05) (Figure 6)

Conclusions 302
During the past decades, breeding for tomato leaf curl virus resistance has been a major 303 focus for the resistance breeding programs in tomato. Therefore, breeding efforts have been 304 made to combine significant resistance to TLCV with important fruit quality and yield 305 traits. The diallel matting design is a popular choice as it helps in the identification of 306 parents with good GCA effects and hybrids with good SCA effects. 307 Additionally, it provides the important information on gene action and inheritance of 308 the traits. In this study, we evaluated seven morphological and three biochemical traits of 309 interest for tomato breeding under leaf curl virus pressure. The high diversity in the 310 material was confirmed by GCA and SCA values for all traits. This showed the significance 311 of both the additive and the non-additive effects in the inheritance of the traits evaluated. 312 Also, we have dissected the inheritance of total yield using the Bayesian approach. It was 313 shown that total yield was more dependent on additive variance than the non-additive 314 variance. Overall, this information will be useful to design and develop breeding programs 315 aiming to improve TLCV resistance along with a respectable combination of important 316 traits. The moderately resistant and high yielding parents (P4 and P9) and hybrids (H23, 317 H42, and H49) could be used for the resistance breeding in tomato . 318

Conflicts of Interest:
The author declares no conflict of interest. 319