Correlation between morphoagronomic traits and resistance to ethylene action in ornamental peppers

The post-production quality of ornamental peppers can be shortened due to exposure to ethylene. The concentration of this phytohormone at 10 μL/L induces leaf, fruit and flowers abscission, ripening of climacteric fruits, organ senescence, seed germination and seedling growth. We evaluated the correlation between pepper morphoagronomic traits and resistance to ethylene on ornamental peppers. Two genotypes, one resistant (UFPB 132), a susceptible (UFPB 134), and two hybrids (DR x PN; 76 x PN) were utilized to assess the susceptibility or resistance to ethylene. The experimental design was completely randomized, with four replications. First, 19 morphoagronomic characteristics were analyzed when the plants had 30% of fruits at the ripe stage. At this stage, the pots were transferred to a room at 25oC with 8-10 μmol/s/m2 of white fluorescent light. Afterwards, the pots were placed in a 60-L container and treated with ethylene at final concentration of 10 μL/L. The plants were exposed to ethylene for 48 hours and then kept at room temperature for further analysis. Afterwards, the number of leaves and fruits was determined at time zero and after 144 hours after end of the ethylene treatment. The Pearson correlation was calculated for each pair of variables and submitted to t-test (p≤0.05). We observed high occurrence of a significant positive correlation (>0.95) between leaf abscission and the anther length, major fruit width, pedicel length, pericarp thickness and dry matter content of the fruits. No significant correlation between fruit abscission and morphological evaluated variables was found. These results show the possibility to use morphological measurements to select plants resistant to leaf abscission induced by ethylene, while for the abscission of fruits, no relation to the morphological parameters evaluated in this experiment was possible to be established.

In relation to genus Capsicum, Ferrão et al. (2011) reported that pepper fruits have great diversity of color, shape and flavor. The market for pepper is quite diverse, from commercialization for fresh consumption, processing and homemade canning.
Beside its use in cooking, some types of Capsicum peppers are used as ornamental plants, since they have characters which give aesthetic value, as variegated foliage, small canopy, erect and intense fruit color contrasting with green foliage (Carvalho et al., 2006).
Generally, during post-production phase, when the pots are taken to a closed and low-luminosity environment, several factors of this environment affect longevity of plants (Hoyer, 1996). Among these factors, the deleterious effect of ethylene on sensitive varieties is one of the limiting causes to commercialize ornamental peppers. Excess of ethylene in the surrounding environment, plants sensitive to ethylene develop abscission of leaves, flowers and fruits (Serek et al., 2006). Segatto et al. (2013) showed that small concentration of ethylene in the environment, 10 µL/L, affected the post-production quality of ornamental C. annuum varieties. These authors also concluded that ethylene caused leaf abscission and fruit abortion at different levels of intensity, and, stimulated the chlorophyll degradation in the leaves of ornamental peppers.
Mao & Motsenbocker (2002) showed that both the ripeness as the abscission of fruits in species of C. frutescens is regulated by ethylene. Villavicencio et al. (2001) reported that pepper and sweet pepper fruits, from C. frutescens and C. annuum, respectively, can be classified as intermediate fruits, between climacteric and non-climacteric, as a result of selection practices in breeding programs and also that the evolution of ethylene and CO 2 during ripening is one characteristic of each Capsicum cultivar.
Correlation evaluation between morphoagronomic traits and resistance to ethylene allows the evaluation of quantitative ratio of a character in relation to another. Naguettini & Pinto (2007) reported that highly correlated variables may not represent cause and effect relationship, but the tendency that the variables present as their joint variation. On the other hand, Ougham et al. (2007), in a review on the control of senescence in plants, reported that senescence is determined by several genes, which act quantitatively and the variability in the synthesis and action of ethylene found in plants affect their morphology and development. Pleiotropy and genetic linkage are causes of correlation between traits (Falconer, 1981) and, according to Cruz & Regazzi (2001), knowledge of correlations between variables is required at different stages of breeding programs, since most breeding programs take into account many features simultaneously, and the correlation between them can contribute to the choice of the most appropriate selection procedures to maximize genetic gain per generation (Santos & Vencovsky, 1986;Ferreira et al., 2012). In this sense, this work aimed to evaluate the correlation between morphologic characters and resistance to ethylene in ornamental peppers.

MATERIAL AND METHODS
The experiment was carried out in a greenhouse, in the laboratory of Plant Biotechnology in Agricultural Science Center of Universidade Federal da Paraíba. Two genotypes (UFPB 132) and (UFPB 134), resistant and susceptible to ethylene, respectively, were used ( Figure 1). And two hybrids (DR x PN; 76 x PN) resistant to ethylene.
Accessions with identification number in germplasm bank of Universidade Federal da Paraíba 134 and 132 are the varieties Calypso and the accession BGH 7073 (Universidade Federal de Viçosa), respectively. They were pre-selected as patterns of susceptibility and resistance to ethylene, respectively (Segatto et al., 2013). The seeds were sown in polystyrene trays of 128 cells, containing commercial substrate (Plantmax ® ). The seedling transplanting was performed to plastic pots with capacity of 900 mL, when the seedlings showed from four to six definitive leaves, using the same substrate for seedling production. Morphoagronomic characterization of Capsicum plants was based on quantitative descriptors list recommended by IPGRI (1995). Nineteen quantitative traits were evaluated, when the plants showed 30% of ripe fruits, as it follows: plant height, first bifurcation height, stem diameter, average leaf length, average leaf width, average leaf petiole length, average corolla length, average petal diameter, average anther length, average filament length, average fruit weight, average fruit length, major fruit width, minor fruit width, average pedicel length, average pericarp thickness, average placenta length, dry mass content and average number of seeds per fruit.
A f t e r m o r p h o l o g i c a l characterization, the pots were transferred to a room at 25°C with 8 -10 µmol/s/m 2 of white fluorescent light. Controls without ethylene were kept in these same conditions for visual comparison of exposed and unexposed plants. Then, the pots were placed in 60 L-sealed containers in the presence of ethylene, at final concentration of 10 µL/L. The plants remained exposed to ethylene for 48 hours, and, afterwards, they were kept at temperature of 25°C with 8 -10 µmol/s/m 2 of white fluorescent light, for further analysis of ethylene effects. The plants were analyzed in relation to number of leaves and fruits at time zero (before the treatment with ethylene) and at 144 hours after the treatment with ethylene for leaf and fruit abscission. Loss of leaves and fruits was expressed in percentage, in relation to time zero, after exposure to ethylene. The experimental design used was completely randomized, with four treatments and four replications. For correlation analysis, values in percentage, of number of leaf and fruit abscission, were determined. Data were subjected to normality test and, when the normality was detected, Pearson correlation analysis was performed. This was calculated for each pair of traits and values subjected to t-test (p≤0.05). All analyses were performed using computer program Genes (Cruz, 2006).

RESULTS AND DISCUSSION
Results show occurrence of high significant positive correlation (>0.95) between leaf abscission and anther length, major fruit width pedicel length, pericarp thickness and dry mass content of fruits (Table 1). These data show that the selection of plants with higher values in any of these traits may cause greater leaf fall, since changes caused between these traits and leaf abscission occur by common factors. Cruz et al. (1988) stated that, in breeding programs, correlation between traits should be taken into account, because changing one trait, by selecting, cause change in another trait related to it. According to Nunes et al. (2008), when the desired character has low heritability or is difficult to evaluate, it is advantageous, in breeding programs, if practice indirect selection, to use another highly correlated character, with high heritability character, and/or easier to evaluate. In the present study, it is possible to state that, in future studies, indirect selection aiming to decrease anther length, major fruit width, petiole length, pericarp thickness and dry mass content traits, result in simultaneous selection of plants with lower leaf abscission caused by the deleterious effects of ethylene. The use of these traits to compose selection indexes may help in obtaining plants resistant to ethylene.
Both leaf (Brown, 1997) and fruit senescence (Mao & Motsenbocker, 2002) are influenced by ethylene. John et al. (1995) in their work with antisense tomato plants showed that ethylene is directly related to leaf senescence. Davies & Grierson (1989) showed that several genes related to fruit ripening are expressed during the leaf senescence process, which suggests similarities between leaf senescence and fruit ripening. In fact, these authors report that accumulation of specific mRNA is common to both processes.
Significant correlations between fruit abscission and morphologic traits evaluated were not observed (data not shown). Given the above, occurrence of fruit abscission, after ethylene exposure, would be expected in this work; however Mao & Motsenbocker (2002) showed that the force required to detach the fruit of the plants was affected by ethylene only when the fruits were at stage 3 of growth (fruit almost fully ripe). In the present study the methodology used by Segatto et al. (2013) was adopted, in which ethylene application occurred when the plants showed 30% of ripe fruits, simulating the stage when the plants are transported and marketed. As in pepper ripening is gradual, 70% of fruits would be at stage 1 (completely green fruit) or 2 (color changing from green to red). Fruit senescence might be detected if ethylene treatment had been done later. Due to the fact that the percentage of fruit senescence has been referring to total fruit, and not to total ripe fruit, it may have led, also, to the underestimation of this trait, which may have result in failure to detect the correlation between the application of ethylene and fruit abscission.
Cultivation and commercialization of potted ornamental peppers have been increasing all around the world (Finger et al., 2012). Segatto et al. (2013), in their study with different genotypes of ornamental peppers, showed that ethylene affected longevity of the plants exposed to this hormone. Serek et al. (2006) reported that the sensitivity level of ornamental plants to ethylene is, generally, defined at family level, but, the differences can be found, also, in the same species. Santos et al. (2013) showed the variation, for resistance to ethylene, in segregating population (F2) of ornamental pepper of Capsicum annuum species. Also, according to these authors, the evaluated genotypes showed different percentages of leaf abscission, genotypes totally sensitive to ethylene and other resistant being found, showing that genetic variability, in the same species, can be noticed, as Serek et al. (2006) recommended.

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programs, for ornamental purpose, plants of smaller fruits and lower pericarp thickness should be selected, since they are more resistant to leaf senescence caused by ethylene.
The authors suggest that, to detect correlation between ethylene sensitivity and fruit senescence, ethylene treatment should be performed when plants have at about 70% of ripe fruits, stage responsive to ethylene and that fruit abscission percentage would be performed in relation to the total of ripe fruits and not to the total of fruits per plant.