Morphological and Physiological Traits in Seedlings’ Populations Obtained from the Hybridization of Promising Genotypes of Quince (Cydonia oblonga Mill.)

Quince (Cydonia oblonga Mill.) is a domestic species of southwestern Europe and Asia Minor (Rodríguez-Guisado et al. 2009). Iran is one of the most important producers of quince in the world. The growing of a single-cultivar in the quince orchard is common, but there are some economic concerns in a single-cultivar orchard, such as pollination and fruit set problems, as well as decreasing quality and yield (Tatari et al. 2018). In single-cultivar quince orchards dominates self-pollination, resulting in flower and fruitlet abscission, which leads to the severe decline of yields (Tatari et al. 2018). The cultivation of several cultivars in the quince orchards can prevent abscission and increase yield. Until then, no purposeful hybridization between promising genotypes were carried out in Iran. In this study, the results of evaluation of quince hybrids at the vegetative phase are presented, with the aim of searching for useful correlations among them.

The highest coefficient of variation was obtained for peroxidase activity and the lowest for leaf length (Table 3). The high coefficient of variation indicates the high diversity in the trait among seedlings from the same crossing. Traits with a high variation coefficient provide a greater chance of passing that trait to offspring. Plant peroxidases are important as they catalyze the reduction of hydrogen peroxide and scavenge reactive oxygen species (Wu et al. 1999). Also, leaf chlorophyll content showed a high coefficient of variation of 23.9%. High variation in peroxidase activity and leaf chlorophyll content were reported by Petrokas and Stanys (2008) and Mohammadi et al. (2014), respectively. Among the morphological traits, canopy width (23.1%) and leaf length (5.8%) had the highest and the lowest coefficient of variation, respectively (Table 3).

Only KVD2 (the highest – 60 cm) and KVD4 × ‘Viduja’ (the lowest – 39.6 cm) seedlings differed significantly in height. All other populations were intermediate (Table 4). The biggest seedling diameter was found in populations from ‘Viduja’ (10.8 cm) and KVD4 (11.1 cm) open pollinations and the lowest in populations from KVD2 × KVD4 and KVD4 × ‘Viduja’ crosses (8.9 and 8.9 cm). Seedlings in population KVD4 × ‘Viduja’ were the lowest with the height and diameter. Both parents of this population were lower than KVD2 genotype and thus their progeny produced lower and thinner shoots.

The biggest annual growth was scored in KVD2 × ‘Viduja’ (9.5 cm) and least in ‘Viduja’ (5.9 cm). Similar dependencies were between these two populations concerning canopy with the exception that the smallest value of this trait was in KVD4 and in KVD2 open populations.

Chlorophyll and Fe contents were negatively correlated (Table 5). The highest Fe content was found in KVD4 open pollinations and significantly lowest in KVD2 × ‘Viduja’, ‘Viduja’ open and KVD2 open populations (Table 4). The highest content of chlorophyll was measured in KVD2 × ‘Viduja’ and significantly lowest in KVD2 × ‘Viduja’ and significantly lowest in KVD2 open and KVD2 × KVD4.

The range of studied traits is shown in Table 3. The range of iron content in the studied populations was from 112 to 224 mg·kg⁻¹ (the studied seedlings were not fed with iron or micro-elements). The range of Fe contents in the study of Abdollahi and Ahmadi (2017) on different quince genotypes were from 75 to 135 mg·kg⁻¹ fresh weight. The range of leaf chlorophyll content was also high – between 1.9 and 3.9 mg·g⁻¹ of fresh weight. Similar range was reported by Rajabpoor et al. (2014) for wild almond species (1.5 to 3.7 mg·g⁻¹ fresh weight). Iron plays an essential role in chlorophyll biosynthesis and the concentration of active iron is directly correlated with chlorophyll content (Sahin et al. 2017), but in the present study, population KVD2 × ‘Viduja’ showed the highest total chlorophyll and the lowest total iron contents. The total iron content in the leaves is not always a reliable parameter for indicating the chlorophyll content, iron availability, and chlorosis. There are reports that iron is stabilized in the apoplastic space of the cell and is not transmitted to the cytoplasm and organelles. Under these conditions, the leaves may show symptoms of chlorosis, which is called the Iron chlorosis paradox (Sahin et al. 2017), so the active iron has a greater role in determining the actual content of available iron of leaves (Samar et al. 2010).

The level of CAT activity was stable within populations and was about 10 nmol·min⁻¹·g FW⁻¹. Only two populations had lower value of this trait – ‘Viduja’ × KVD4 (7.5) and ‘Viduja’ open (9.2) (Table 4). Both populations had ‘Viduja’ as mother.

Enzymes such as peroxidase, which appear in different isoforms in the cell, scavenge reactive oxygen species. The activity of this enzyme continues throughout the life of plants from germination to the aging stages participating in the control of cellular elongation, defense mechanisms and several other functions (Wu et al. 1999). In three populations, where KVD4 was in maternal position had the highest peroxidase activity (70.7 to 64.5 nmol·min⁻¹·g FW⁻¹). The lowest POD value was in populations where ‘Viduja’ was in the maternal position (17.9 and 25.1 nmol·min⁻¹·g FW⁻¹).

Correlation of traits is used to investigate a logical and meaningful relationship between traits (Table 5). According to the results, the correlation among most traits was not significant and only some traits showed high correlations. Seedling height was positively and significantly correlated with chlorophyll index, canopy width with annual growth and leaf length, and the total iron content in leaves showed a significant positive correlation with catalase activity. Catalase is one of the most important hydrogen peroxide neutralizing enzymes in plants. This enzyme contains iron as a cofactor in its structure and its activity is reduced under iron deficiency. Correlations between this enzyme activity and leaf iron content have also been reported previously (Sun et al. 2007). For some species, a positive linear relationship between the chlorophyll index and total extractable leaf chlorophyll has been determined (Marquard & Tipton 1987), but this relationship was not confirmed in the present study.

The studied populations were classified into four distinct groups at 10 squared Euclidean distance based on the Ward method (Fig. 1). ‘Viduja’ open pollination, ‘Viduja’ × KVD4, KVD2 × ‘Viduja’ and KVD2 × KVD4 populations that one of their parents was ‘Viduja’ or KVD2, were placed in the same group. The same levels of seedling height, seedling diameter, and chlorophyll index, as well as lower total iron content, were characteristic for this group.

Figure 1

The progeny of KVD2 and KVD4 open pollination were classified in the second group. The progeny of these populations were similar in values of seedling height and diameter, canopy width, annual growth increase and catalase activity, and showed the lowest leaf chlorophyll content.

KVD4 × ‘Viduja’ and KVD4 × KVD2 populations that had the same female parent were placed into separate groups. In the third group, population KVD4 × ‘Viduja’ was placed. The lowest length and diameter of shoots belonged to the progeny of this population. Population KVD4 × KVD2 was in the fourth group and had the lowest canopy width and highest catalase and peroxidase activity. It seems that the same female parents had not led to similarities between progeny in all populations.

At this moment, it is not possible to predict which of the analyzed at the vegetative stage traits can be markers for the future fruit yield. The observation will be carried out every year up to the stage of full yielding.