Multivariate analysis to assess abscisic acid content association with different physiological and plant growth related traits of Petunia

Petunia is an important and beautiful ornamental flowering plant, grown throughout the world for its beauty and attraction. Different Petunia hybrids have been developed by petunia growing countries of the world. The prescribed study was conducted to investigate the association of abscisic acid with seed yield and its contributing traits of petunia line. Data for different physiological, morphological and petunia seed yield traits was recorded, analyzed and interpreted for final inferences. From results it was showed that the petunia lines IAGS-P8, IAGS-P9 and IAGS-P11 performed well for most of the studied traits. It was shown from multivariate analysis techniques that stomata conductance, chlorophyll b contents, seed area, chlorophyll a contents, flower fresh mass, flowers per plant, seed mass and abscisic acid contributed higher to seed yield per plant in petunia. The abscisic acid contents showed positive and significant association and contribution towards seed yield of petunia genotypes. It was suggested that selection on the basis of abscisic acid may be useful to develop good seed yield per plant and large number of flowers per plant in petunia under stressful environmental conditions.


INTRODUCTION
The genus Petunia is an important ornamental plant of high economic imperativeness on the whole agriculture.It gives dominant qualities to serve as model plant for contemplating plant improvement.The history of Petunia development as a crop is accent with implications for an advanced array of added ornamental crops (Cantor et al., 2015;Gerats and Vandenbussche, 2005).This generally developed genus of flowering plants fits in with Solanaceae gang.It is an important ornamental plant in landscape because of colour diversity.A large number of hybrids and varieties have been developed with diverse color and patterns (Ganga, 2011).This plant is native to Brazil, Argentina or Uruguay and included over 35 species (Dole and Wilkins, 1999).Petunias are considered an annual ornamental plant but may be perennial in warmer climates (Berenschot et al., 2008).Petunia genus includes about 20 species of South American origin, mostly perennials but developed as annuals (Mallona et al., 2010), 14 annual species (Toma, 2009), but Petunia hybrida Hort.(P.axillaris Lam.× P. violacea Lindl.) is a species which presents the biggest decorative value (Berenschot et al., 2008;Vandenbussche et al., 2016).Presently the researches have also confirmed that the genus Petunia is consisted of 14 closely related species (Stuurman et al., 2004).The modern petunias have been developed through hybrid breeding like the violet petunia (P.violacea, and P. integrifolia (Hook.)Schinz & Thell.) and ambrosial agrarian or white petunia (Petunia axillaris).A large number of researchers are also working on finding the real ancestors because their ancestors are rarely cultivated today.Petunia is a small sprawling plant with large number of flowers, grown throughout the world for its beauty and interactive colors (Anderson, 2006;Băla, 2007).Petunias blossom abundantly even in hot summers and new varieties even in seasons with top clamminess (Băla, 2007;Florin et al., 2012).The petunia is long day plant due to which it is used for landscape proposes (Anderson, 2006;Currey and Lopez, 2013).The present study was conducted to develop inbred lines of petunia through selfing for growing seasons.The data of various morphological, physiological and seed yield traits was recorded to access the performance of inbred lines under development.The identification of promising inbred lines for the development of petunia hybrids.

RESULTS AND DISCUSSION
The results from Table 1 persuaded that significant differences among all the studied traits were found.The highest heritability (h 2 bs) was found for photosynthetic rate, sub-stomata CO 2 concentration, stomata conductance, water use efficiency, plant height, leaves per plant, flowers per plant, seeds per fruit, leaf area, seed yield per plant and abscisic acid contents.The genetic advantage was found higher for all studied traits except sub-stomata CO 2 concentration, flowers per plant, seeds per fruit, seed mass while moderate for abscisic acid content and leaves per plant.The higher broad sense heritability referred the dominance type of gene action and suggested that the selection for such traits may be helpful to develop petunia hybrids with much of vigor and ability to tolerate harsh environmental conditions as higher value of h 2 bs was recorded for abscisic acid content.Higher concentration of abscisic acid contnets in plant body gives an extra advantage to grow in drought conditions with higher and well performance.Various researchers while working on different crop plants have described about higher heritability for these traits as reported in our study (Aaliya et al., 2016;Ali et al., 2015;Ali et al., 2013;Ali et al., 2014a;Mahmood and Haider, 2016).Genetic advance indicated the presence of additive type of gene action hence the traits with higher genetic advance suggested that the selection of lines may also be helpful to develop synthetic varieties.The similar findings for different crops have been reported by various researchers (Ali and Ahsan, 2015;Ali et al., 2014b;Ali et al., 2014c;Khorasani et al., 2011;Mahmood and Haider, 2016).The results (Supplementary Material Table S1) indicated that the lines IAGS-P8, IAGS-P9 and IAGS-P11 were better performing than all of the other lines also seen form figure 1a (principal component analysis) that the lines IAGS-P2, IAGS-P8, IAGS-P9 and IAGS-P11 fall in quadrant I which indicates the highest and best performance for respective traits.The lines which showed the best performance may be used for the development of good quality cultivars, with large number of flowers, stress tolerant and multicolor petunia hybrids and varieties (Ali et al., 2013;Florin et al., 2012;Mahmood and Haider, 2016).The correlation analysis provides best opportunity to the researchers for selecting genotypes of crop plant to improve crop plant growth and production (Ali et al., 2016;Ali et al., 2014c).The results from table 2 indicated that significant correlation was found for photosynthetic rate with chlorophyll a contents, plant height, sub-stomata CO 2 concentration, leaf width, abscisic acid and seeds per fruit.Abscisic acid contents was found to be significantly correlated with most of the studied traits including photosynthetic rate, chlorophyll a contents, chlorophyll b contents, plant height, substomata CO 2 concentration, transpiration rate, water use efficiency, leaf temperature, leaf area, leaf width, fresh shoot mass, seeds per fruit, 100-seed mass, seed mass and seed yield per plant.Seed yield per plant was significantly correlated with photosynthetic rate, transpiration rate, leaf temperature, leaves per plant, fresh leaf mass, stem diameter, seed area, seed mass, seeds per fruit, flowers per plant and abscisic acid contents.The positive and significant correlation revealed that the selection of lines to develop hybrids and synthetic varieties may be helpful to improve the growth and development of petunia.The significant correlation of abscisic acid content with morphological traits, seed yield and physiological traits indicated that the selection of petunia lines on the basis of good abscisic acid production may be fruitful to improve drought tolerance in petunia (Aaliya et al., 2016;Abbas et al., 2016;Filipović et al., 2014).
The growth of petunia was adversely affected by changing the environmental optimum temperature of 25 °C with minimum circadian light intensity to be 13 Wm -2 (Kaczperski et al., 1991).It has been observed that temperature and light caused major effects on growth and development of petunia.Therefore, new petunia varities and hybrids should be developed which can tolerate varying environmental conditions to continue optimal plant growth and development.
However, the holdup of plant growth, development, the access of CO 2 by stomata in an optimized environmental condition has shown not any extensive adverse effect on petunia plants (Blanchard and Runkle, 2009).
Stepwise regression analysis was performed to predict the trait(s) that were highly contributing towards the petunia seed yield per plant.
Stepwise regression analysis provides an opportunity to select crop plant genotypes with higher contribution traits to improve crop yield and production (Aaliya et al., 2016;Abbas et al., 2016).The results from The use of PCA (principal component analysis) to overcome the error effect of large number of independent variables in breeding experiments and find overall attributed variation in dependent structure (Ali et al., 2015;Filipović et al., 2014;Goodarzi et al., 2015;Marjanović-Jeromela et al., 2011).It has also been reported that the eigenvalues (in PCA) showed primary significance for numerical diagnostics to evaluate variation endorsed by a large number variables on the dependent structure and their data matrix in a graphical display (Greenacre, 2010).Therefore, we have also performed principle component analysis (PCA) to inspect the traits which were contributing higher towards petunia seed yield per plant.Our data generated four PCA as shown in Table 4 with diverse variation among all of the studied traits.It was found that the PC1, PC2, PC3 and PC4 contributed variation of 35.60 %, 24.60 %, 17.90 % and 11.3 % while their cumulative proportion was 25.2 %, 43.20 %, 57.20 % and 73.10 % respectively.PC1 and PC2 contributed higher variation for respective studied traits (Fig. 1a) the eigenvalues of these four PCs was higher than 1 (Fig. 1b).The Figure 1a also showed that the petunia lines IAGS-P2, IAGS-P8, IAGS-P9 and IAGS-P11 showed better performance for most of the studied traits.Principal factor analysis was performed by using principle component analysis values, to check that traits which were directly contributing and highly associated with petunia seed yield per plant.The factor 1 was found to be highly contributing factor trait which contributes 48.20 % in total variation were chlorophyll a, chlorophyll b, transpiration rate, stomata conductance, leaves per plant, water use efficiency, leaf area, leaf length, seed yield per plant stem diameter and abscisic acid content (Table 5).Abscisic acid content and seed yield per plant were found the most contributing traits of petunia.Various researchers have suggested that the selection of crop plant genotypes on the basis of the factor analysis (traits from factor 1) may be supportive to develop higher yield hybrids and synthetic varieties of crop plants.While the traits which fall in factor 2 (from factor loading table 5) indicated that the selection of crop plant genotypes on the basis of such traits will not be helpful as the segregation will take place in the next growing generations (Ali et al., 2016;Filipović et al., 2014;Mahmood and Haider, 2016).The better performance of petunia lines for chlorophyll a, transpiration rate, chlorophyll b, leaves per plant, stomata conductance, leaf length, water use efficiency, leaf area, stem diameter, seed yield per plant, seed mass and abscisic acid content revealed that the accumulation or assimilation of organic matter/compounds will be higher in the plant body.It has been also found the accumulation or assimilation of organic biomass in plant body is very essential for the proper enhanced growth and development of petunia plant (Hladni et al., 2011;Huang, 2007;Huang and Yeh, 2009;Mahmood and Haider, 2016).The accumulation of organic compounds generally takes place in the leaves, stem and flowering parts of a plant body.The results from our study were well supported by results which demonstrated the role of factor analysis for effective selection criteria in maize breeding program (Filipović et al., 2014).In order to understand about the genetic association among petunia lines, cluster analysis was performed (Khorasani et al., 2011;Mostafavi et al., 2011).The results from clustering showed that the petunia lines IAGS-P2 and IAGS-P12 followed by IAGS-P8 and IAGS-P9 were highly associated with each other as compared with other petunia lines (Fig. 2a) the association was verified through the development of minimum spanning tree (Fig. 2b) that showed smaller distance between petunia lines IAGS-P8 and IAGS-P9 while IAGS-P2 and IAGS-P12 were having IAGS-P1 in between them through the use of eigen values.So, from results it may be revealed that the petunia lines IAGS-P8 and IAGS-P9 were highly associated with each other and may be used as two separate male or female lines to develop petunia hybrids as also verified by mean performance and principal component analysis Figure 1a results of these lines.Also the petunia line IAGS-P11 showed better performance for almost all under studied traits, so it may also be used as male to develop good quality petunia hybrids (Mahmood and Haider, 2016).It was also suggested that in future breeding program of IAGS-P8, IAGS-P9 and IAGS-P11, these traits may be important for primary selection of synthetic petunia varieties and hybrids to increase seed yield per plant of petunia under various environmental regimes of Pakistan and other growing countries.Moreover, the hybrid seed production technology proved to be more efficient as it reduced the cost, time and increase efficacy for better selection in petunia improvement programs.Still, further studies are required which should cover different years and locations.

Figure 2 :
Figure 2: a. Dendrogram analysis based on hierarchal clustering.Association of petunia lines on genetic basis of all studied traits, b.Minimum spanning tree using eigene values for petunia lines on the basis of all studied traits

Table 2 :
Correlation among various morpho-physiological and yield traits of petunia

Table 3 :
Stepwise regression analysis for various traits of petunia for seed yield

Table 4 :
Principal component analysis

Table 5 :
Factor loadings for different traits of petunia