Xiaoxia HAN, Xinjun HU, Jianwen SU, Zuhua YUAN, Yongqi LI

The Vegetable Engineering Technology Research Center of Hunan Province/Hunan Vegetable Research Institute, Changsha 410125, China

Pumpkin (Cucurbita moschata),one of the four main cultivated species in genus Cucurbita,has wide adaptability, long shelf life and is thus widely planted and processed in China[1-2].Owing to excellent nutrition and rich active ingredient, the meat used old pumpkins, most of which are local cultivars, are precious resources in China[3-8]. According to some statistics, 1 046 native pumpkin germplasm accessions had been collected by 1995,but most of them have not been researched and classified[9].In 2007, Zhou et al.[10]analyzed some botanical traits of 123 climbing pumpkin inbred lines,and proposed the representative traits to evaluate climbing pumpkin cultivars. Through grey correlation analysis, Li et al.[11]measured 10 economic traits of 129 pumpkin hybrids to determine which one had the most significant correlation with fruit weight, soluble solid content, the first female flower node and fruit shape during 2009, also investigated the importance of stem diameter in pumpkin breeding. The correlations between nutrient content and fruit characters of pumpkins grown in greenhouse proposed by Liu[12]also provided some references for pumpkin breeding. In 2010, Zhou et al.[13-14]analyzed and e valuated the traits of 24 pumpkin germplasm accessions, such as seed traits, seedling traits, fruit maturity,yield and fruit quality, and found that there were abundant diversity in Chinese pumpkin cultivars. The correlation of eight agronomic traits of 50 pumpkin inbred lines were analyzed by Du et al.[15],and the results provided a reference for comprehensive evaluation on pumpkin traits at early growth stage. The survey by Liu et al.[16]on virus diseases in 52 pumpkin inbred lines provided scientific basis for the breeding of virus-resistant pumpkin cultivars. Li[17]et al. evaluated the agronomic and fruit traits of 20 pump-kin cultivars from South China to provide scientific basis for their promotion and cultivation. Besides, the diversity in 37 pumpkin germplasm accessions was evaluated by Yuan et al.[18]. The correlation and cluster analysis were conducted among 16 agronomic traits of 46 pumpkin inbred lines by Sun et al.[19]in 2013. A series of Baimi pumpkin cultivars were developed and evaluated by Li et al.[20].

As we could see from the studies above, the main botanical traits and correlations of some pumpkin cultivars have been measured and analyzed,which provided theoretical basis their utilization. To fully learn the genetic background of breeding materials, the main representative pumpkin cultivars all over the country should be evaluated and compared.Therefore,the main botanical characters of 41 pumpkin cultivars from 16 institutes were measured for diversity, correlation and cluster analysis in the present study,aiming at providing basis for choosing excellent traits and parental materials during pumpkin breeding process.

Materials and Methods

Time and site

This study was carried out in the experimental field,locating of Gaoqiao Base in Xingsha Town,Changsha City in March, 2013. The seeds were selected in a hanging storage room of Gaoqiao Base in July,2014.

Materials

As shown in Table 1, 41 pumpkin cultivars from the Pumpkin Exhibition of Horticulture Society were selected as the experimental materials.

Methods

Experimental design Field trials were carried out in Gaoqiao Base of the Institute of Vegetables, Hunan Academy of Agricultural Sciences.The base was newly developed, with shallow layer of tillage soil.The 41 cultivars were sown in greenhouse on March 20, 2013, and the seedlings were transplanted into open field on April 12, groveling on the ground. Forty plants of two cultivars were planted in each plot,spacing 0.6 m to each other.The plots were arranged at random.Their major agronomic traits, such as initial flowering date, the first fruiting node,stem diameter,internode length,transverse and longitudinal diameters of the largest leaf and fruit setting rate were recorded and measured in detail.Five plants were randomly selected and harvested at maturity to measure their single fruit weight, fruit length,fruit stalk length,fruit transverse diameters at lower and upper parts, flesh thickness and soluble solid content.

Table 1 Information of the 41 pumpkin cultivars tested in this study

Experimental machine A hand held refractometer (Chengdu, 0.2% ), a desktop electronic scale (Chengdu,0.01 g) and a tape measure (Changsha, 0.1 cm) were the major tools for measuring the agronomic traits of pumpkins.

Statistics analysis All the data were statistically analyzed by Excel andcluster analysis was performed using SPSS10.0.

Results and Analysis

Variations in botanical characters among the 41 pumpkin cultivars

Among the main agronomic traits,fruit stalk length showed the largest variation, up to 43.23% among these pumpkin varieties. The fruit stalk length of the cultivars was 13.33 cm on average, ranging from 5.0 cm (C1578 and XMZ-1) to 40.5 cm (2012-1). Except fruit stalk length, fruit weight, fruit length and flesh thickness also exhibited large variations among the cultivars, they were 24.48%, 21.62% and 20.70%.For example,the mean of single fruit weight was 3.35 kg, while that of cultivar 2012-4 was the smallest,only 1.10 kg, and that of Shanmei No.3 was the largest, up to 4.75 kg. The single fruit weight of 23 pumpkin cultivars, accounting for 56.1% of the tested materials, varied in a small range from 3.0 to 4.0 kg (Fig.1). The fruit length of the 41 cultivars was 34.04 cm on average,ranging from 58(2012-1)to 24.0 cm(Quanguan No.1).Their flesh thickness ranged from 1.7 cm (2012-2) to 4.6 cm (CP1578), with an average of 3.17 cm.The coefficient of variation in soluble solid content of these pumpkin cultivars was 14.44%.The soluble solid content of Combination-5 and Shanmei No.38 was the largest, up to 10.0%, and that of 25 cultivars was less than 8.0% (Fig.2).Besides, the coefficients of variations in stem diameter, fruit transverse diameter at lower part, the transverse and longitudinal diameters of the largest leaf were 11.38% , 10.00% ,10.25% and 11.06%, respectively. Initial flowering date had the smallest coefficient of variation, only 0.56%. All the data were listed in Table 2.

Table 2 Main agronomic traits of the 41 pumpkin cultivars

Correlations between the botanical characters of pumpkin cultivars

As shown in Table 3, the main botanical traits of the 41 pumpkin cultivars shared significant, or extremely significant correlation with each other.Among them, single fruit weight had an extremely significant positive correlation with fruit transverse diameters of at lower and upper parts,flesh thickness,the first fruiting node,initial flowering date, stem diameter, internode length, transverse and longitudinal diameters of the largest leaf had,a positive correlation with fruit length, but a significant negative correlation with fruit stalk length, and a negative correlation with soluble solid content.Fruit length had an extremely significant positive correlation with fruit stalk length, a positive correlation with single fruit weight and internode length,and a negative correlation with several traits including fruit transverse diameters at lower and upper parts, flesh thickness and soluble solid content.Fruit stalk length shared a an extremely significant positive correlation with fruit length, a positive correlation with soluble solid content,an extremely significant negative correlation with fruit transverse diameters at lower and upper parts and flesh thickness.A significant positive correlation existed between single fruit weight and the first fruiting node. The fruit transverse diameters at lower and upper parts had an extremely significant positive correlation with single fruit weight, flesh thickness, but an extremely significant negative correlation with fruit stalk diameter. Flesh thickness had an extremely significant positive correlationwith single fruit weight, fruit transverse diameters at lower and upper parts,initial flowering date and the first fruiting node, but an extremely significant negative correlation with fruit stalk length. Soluble solid content had an extremely positive correlation with the first fruiting node,a positive correlation with fruit stalk length, fruit transverse cross diameters at lower and upper parts, flesh thickness, stem diameter and internode length. Initial flowering date had an extremely correlation with single fruit weight, fruit transverse diameters at lower and upper parts and flesh thickness, but a negative correlation with fruit length, fruit stalk length and soluble solid content. The first fruiting node had an extremely significant positive correlation with single fruit weight, fruit transverse diameters at lower and upper parts, flesh thickness and stem diameter, and a positive correlation with soluble solid content, and a negative correlation with fruit length and fruit stalk length. Stem diameter had an extremely significant positive correlation with single fruit weight, fruit transverse diameters at lower and upper parts,flesh thickness,a positive correlation with soluble solid content, and a negative correlation with fruit stem length and fruit length.Internode length shared an extremely significant correlation with fruit weight,fruit transverse diameters at lower and upper parts, flesh thickness, and a positive correlation with initial flowering date and soluble solid content. The transverse and longitudinal diameters of the largest leaf had an extremely significant positive correlation with single fruit weight,fruit transverse diameters at lower and upper parts, flesh thickness, the first fruiting node and stem diameter.

Table 3 Correlation analysis of botanical characters of the 41 pumpkin cultivars

Cluster analysis of the agronomic traits of pumpkin cultivars

Cluster analysis on the 41 pumpkin cultivars was performed based on the 13 agronomic traits measured above (Fig.3). The results revealed that all the 41 cultivars were divided into three groups. As shown in Table 4,the single fruit weight, flesh thickness,fruit transverse diameters at lower and upper parts, stem diameter, internode length, transverse and longitudinal diameters of the largest leaf in Group 1,which included 90.24% of the tested cultivars, were better than those in Group 2 and Group 3. The cultivars in Group 1 shared close relationship witheach other and a high similarity over 95%. The only cultivar (2012-1) of Group 2 had longer fruit,fruit stalk and higher soluble solid content than other groups.The three cultivars(Quanguan No.1,2012-3 and 2012-4)of Group 3 and the only cultivar of Group 2 began to flower and bear fruit earlier than those of Group 1, but their single fruit weight, flesh thickness and soluble solid content were significantly lower than those of Group 1(P=0.001).

Discussion and Conclusion

The results revealed that there were large variations in the fruit stem length, single fruit weight, fruit length,flesh thickness and the first fruiting node,but smaller variations in stem diameter, fruit transverse diameter at lower part, transverse and longitudinal diameters of the largest leaf among the 41 pumpkin cultivars. The large variation in fruit length and the small variation in stem diameter were consistent with the findings of Sun et al.[19].In the present study,single fruit weight and soluble solid content were also evaluated, and the results indicated that the single fruit weight of most cultivars was above 3 kg, even reaching to 4.75 kg, but the soluble solid content of most cultivars was relatively low.The reason why this consequence happened may be that fruit weight was considered as an important index in breeding process, while soluble solid content was not. So, more attention should be paid to improve soluble solid content in future work.

Correlation analysis revealed that there was significant or extremely significant correlation between these agronomic traits. For example, single fruit weight had an extremely significant positive correlation with fruit transverse diameters at lower and upper parts, flesh thickness, the first fruiting node,stem diameter,internode length, transverse and longitudinal diameters of the largest leaf, indicating that fruit weight can be improved depending on these traits. Fruit length had a significant positive correlation with fruit stalk length, single fruit weight and internode length.Fruit stalk length had a significant positive correlation with fruit length and soluble solid content.Single fruit weight and the first fruiting node were significantly and positively correlated with each other.Fruit transverse diameters at lower and upper parts had an extremely significant positive correlation with single fruit weight, flesh thickness, initial flowering date and the first flowering node. Flesh thickness shared an extremely significant positive correlation with single fruit weight, fruit transverse diameters at lower and upper parts and initial flowering date. Soluble solid content had a positive correlation with the first fruiting node, fruit stalk diameter, fruit transverse diameters at lower and upper parts and flesh thickness.Initial flowering date had an extremely significant positive correlation with single fruit weight,fruit transverse diameters at lower and upper parts and flesh thickness. The first fruiting node was positively correlated with fruit weight,fruit transverse diameters at lower and upper parts and flesh thickness. Stem diameter was also positively correlated with single fruit weight, fruit transverse diameters at lower and upper parts and flesh thickness. Internode length had an extremely significant positive correlation with single fruit weight, fruit transverse diameters at lower and upper parts and flesh thickness. Transverse and longitudinal diameters of the largest leaf had an extremely significant positive correlation with single fruit weight, fruit transverse diameters at lower and upper parts, and flesh thickness.All the results indicated that it is possible to improve some special traits through other traits positively related to them.

The cluster analysis of the 41 pumpkin cultivars indicated that Group 1 included more than 90% of the total,and they shared close genetic relationship.Only one cultivar 2012-1 was divided into Group 2 and three(Quanguan No.1, 2012-4 and 2012-3) into Group 3. The results above demonstrated the narrow genetic background of exiting pumpkin germplasm,and the materials with similar genetic back-ground were selected in breeding. So,it is urgent to broaden the genetic background in pumpkin breeding.

According to the variation, correlation and cluster analysis of main botanical traits among the 41 pumpkin cultivars, we found that there were large variations in fruit stem length,single fruit weight,fruit length and flesh thickness, but small variations in initial flowering date, stem diameter, fruit transverse diameter at lower part,transverse and longitudinal diameters of the largest leaf. Most of the traits shared significant,or extremely significant correlation with each other. The cluster analysis indicated that the 41 pumpkin cultivars in three groups had a high similarity,indicating their narrow genetic background. So, it is essential to introduce new materials and broaden the genetic background for pumpkin breeding.

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