Agronomic, physical and chemical characterization of banana fruits

The purpose of this study was to characterize 26 banana accessions of the active genebank of Embrapa Cassava and Tropical Fruits (Brazil) for agronomic, physical and physicochemical characteristics. The plant height of the diploid 028003-01 and triploid Walha was short. Regarding the number of fruits and bunch weight, the triploids Caipira, Thap Maeo and the tetraploids Ambrósia and Calipso performed particularly well. Total carotenoid contents were highest in the diploids Jaran and Malbut. The total contents of flavonoid and polyphenol, two natural antioxidants, were highest in tetraploid Teparod. Wide genetic variability was detected for most agronomic, physical and chemical characteristics of the fruits of the banana accessions, enabling the planning of breeding for the development of hybrids with short stature, high yield, pest resistance and high carotenoid, flavonoid and/or polyphenol contents.


INTRODUCTION
Banana is the second most consumed fruit in Brazil, second only to orange.In relation to its social role, the crop is exploited by rural small-scale enterprises, ensuring the labor retention and recruitment in the country, representing a source of continuous income.Brazil is the fourth largest producer of banana, with a production of 7.0 million tons in 2007, in an area of approximately 500´000 ha.In the same period, India produced 11.7 million tons on 400´000 ha (FAO 2010).The low productivity in Brazil is a result of the lack of commercial varieties that combine short stature, drought and cold tolerance, good post-harvest characteristics and pest resistance (Silva et al. 2002a).
Typically, banana production is based on triploid cultivars, although diploids are important as allele sources for resistance/tolerance to biotic and abiotic factors (Jenny et al. 1999).Banana breeding programs with these genotypes, which are crossed with commercial triploid cultivars, have generated promising tetraploid hybrids with good performance for the agronomic traits of interest and high physical and chemical fruit quality (Silva et al. 2002a).The information of the agronomic, physical and chemical characterization of banana fruit is useful both for the choice of parents for crosses, and in the selection of diploid elites for the development of improved hybrids.The objective of this study was to characterize the agronomic, physical and chemical characteristics of 26 diploid, triploid and tetraploid banana accessions.
LA Mattos et al.

Plant material
From the Active Genebank of Musa (banana BAG) Embrapa Cassava and Tropical Fruits, Cruz das Almas (BA), 26 banana accessions were used, including wild diploid and improved, triploid and tetraploid genotypes (Table 1).

Agronomic characterization
The experiment was conducted from April 2007 to June 2008.An orchard was planted in 3 m x 2 m spacing, irrigated and treated with cultural practices according to technical recommendations.At least three plants (replications) per accession were evaluated in a completely randomized design.The following traits described by Silva et al. (2002a) were evaluated: plant height in m (PLH), stem diameter in cm (SteD), number of tillers at flowering (NTF), number of leaves at harvest (NLH), stalk length in cm (StaL), stalk diameter in mm (StaD), stalk weight in g (StaW), number of hands per bunch (NHB), number of fruits (NFR), bunch weight in kg (BUW).
Yellow Sigatoka was evaluated under natural infestation in the field at flowering (YSF) and at harvest (YSH), following the methodology proposed by Stover (1972), modified by Gauhl et al. (1993).The following descriptive scale was used: 0 for no symptoms; 1 for symptoms on 1-10% of the leaf; 2 for symptoms on 11-30% of the leaf; 3 for symptoms on 31-50% of the leaf; 4 for symptoms on 51-70% of the leaf; 5 for symptoms on over 70% of the leaf.

Physical and chemical fruit characterization
The following physical characteristics were analyzed: fruit length in cm (FRL), fruit diameter in cm (FRD), fruit weight (FRW) and flesh weight (FLW) in g, flesh diameter in cm (FLD), peel thickness in mm (PTH); flesh firmness in Lb (FLF), soluble solids content, in °Brix (SS), pH and titrable acidity (TAC), according to AOAC (1997).
For chemical fruit analysis, the flesh was sampled in the middle and at both ends of each fruit.The pieces were ground in a household blender with water, at a ratio of 1:2 (flesh: water) (Dadzie and Orchard 2003).
Vitamin C (VIT) was analyzed following the methodology proposed by Terada et al. (1979) in mg 100g -1 and the total carotenoids (CTN) were evaluated according to Rodriguez-Amaya (1999) in μg g -1 .For flavonoid analysis in mg 100g -1 (FLA), the method of Rijke et al. (2006) was used.Polyphenol in mg 100g -1 (PLF) was extracted from the samples in 50% methanol and 70% acetone solutions, as described by Larrauri et al. (1997) and quantified in a spectrophotometer using the reagent Folin-Ciocauteau, according to the methodology of Obanda and Owuor (1997).

Analysis of agronomic, physical and chemical fruit characteristics
Data normality and homoscedasticity were tested for the analysis of variance and grouping of accessions according to the Scott and Knott (1974)'s test modified by Bhering et al. (2008), using the software Genes (Cruz et al. 2006).The variables YSF and YSH were transformed into 5 .0 + x .The mean Euclidean distance among the 26 banana genotypes was estimated, considering the 26 agronomic and physicochemical fruit characteristics.The means were grouped by the UPMGA method using software Genes.

RESULTS AND DISCUSSION
The F test analysis of variance revealed significant differences between the means of banana accessions for most agronomic traits, except for the number of tillers at flowering (NTF) (Table 1).The coefficient of variation ranged from 9.12% (SteD) to 57.08% (NTF).These values are within the range observed by Amorim et al. (2009a) and Amorim et al. (2009b) for the same characteristics.
The plant height (PLH) ranged from 1.44 m for the triploid Walha (AAB genome) to 3.54 m for tetraploid hybrid Ambrosia (AAAA genome), with a mean of 2.79 m (Tableo1).The grouping test of Scott and Knott (1974) formed four groups; the improved diploid 028003-01 (Tuugia x Calcutta) and triploid Walha were classified in the last group, with the lowest values for this character.Results indicated wide genetic variability for plant height among the accessions tested, a positive factor for improving this fruit plant, since it is possible to identify diploid parents for hybridization targeting the development of short-stature hybrids.
The mean stem diameter (CPD) was 17.76 cm, with highest values for the triploid Champa Madras and tetraploids Ambrosia and Calipso of the first group (Tableo1).This trait is related to the vigor and crack resistance of the pseudostem, reflecting the support capacity of the bunch.Genotypes with greater stem diameter are less susceptible to lodging (Silva et al. 2002a, Donato et al. 2003).Since the diploids are thin plants, the mean SteD was low, with lowest values observed for 028003-01and IDU-110, classified in the last group.
Regarding the number of leaves at harvest (NLH), the mean was 6.77, and two groups were formed (Table 1).The highest mean value was 9.20 leaves for the cultivars Tropical and Maravilha and the lowest 2.00 leaves for genotype Towoolle.It is known that fruit filling (size) is directly correlated with the number of green leaves at harvest.According to Soto Ballestero (1992), cultivars of the subgroup Cavendish generally need at least eight active leaves per plant for good fruit development.
For stalk length (StaL), the shortest stalk (14.67 cm) was observed for accession 'Tuugia', while Champa Madras had the longest (70.00 cm).A direct relationship between stalk diameter (StaD) and stalk weight (StaW) was observed, with higher values of the hybrids Ambrosia and Calipso (Tables 1 and 2) and shortest stalk diameter and weight of the diploid Tuugia.
Table 1.Means of six agronomic traits in 26 banana accessions of the active genebank of Embrapa PLH: plant height (cm), SteD: stem diameter (cm), NTF: tillers at flowering, NLH: number of leaves at harvest, StaL: stalk length (cm), StaD: stalk diameter (mm); * significant at 5%. # Means followed by the same letter, in the columns, belong to the same group by the clustering test of Scott and Knott (1974), at 5% probability.
Table 2. Means of six agronomic traits in 13 accessions of the active banana genebank of Embrapa StaW: stalk weight (kg), NHB: number of bunches, NFR: number of fruits, BUW: bunch weight (kg), YSF: Yellow Sigatoka at flowering, YSH: Yellow Sigatoka at harvest; * significant at 5%. # Means followed by the same letter, in the columns, belong to the same group by the clustering test of Scott and Knott (1974), at 5% probability.
The number of hands (NHB) and fruits (NFR) per bunch were in the mean 6 and 83, respectively (Table 2).The number of fruits was highest for the triploids Caipira (138) and Thap Maeo (158), tetraploids Ambrosia (154) and Calipso (138) and the diploid Jaran (148), classified in the first group.The characters number of hands and fruits are of great interest for the producer and fundamental for the genetic improvement of banana, since the bunch (fruits) is the commercial unit.Besides, an increase in the number of hands can result in a higher bunch weight, a character that expresses the productivity of a genotype (Silva 2002b, Silva et al. 2003).Similar results were observed for bunch weight (BUW), since this character is related to the number of fruits per bunch and the mean weight of each fruit.
In the evaluation of yellow Sigatoka four groups were formed at flowering and three groups at harvest.Disease resistance was observed in most genotypes, with the exception of diploids Jaran and Malbut.Results show that it is possible to plan new combinations involving diploid and tetraploid genotypes to breed new cultivars with good agronomic characteristics and resistance to yellow Sigatoka (Table 2).
Except for titrable acidity, significant differences and group formation were stated for all physical and chemical characteristics (Tables 3 and 4).The coefficients of variation ranged from 0.86% for flavonoids to 31.24% for fruit weight.
(13.24 cm) and diploids (10.98 cm).A similar performance was observed for the mean fruit diameter and weight and flesh weight and diameter, which formed four, three, three and four groups, respectively.Similar results were reported by Lima et al. (2005), who assessed banana triploid and tetraploid genotypes and found a variation in fruit length of 13 -18 cm and a mean fruit diameter of 3.0 cm.
The mean solids content was 19.48 °Brix, with a range of 14.60 °Brix (triploid Towoolle) to 25.70 º Brix (tetraploid Teparod).Three groups were formed by the Scott and Knott test.These results were similar to those described by Soto Ballestero (1992) for banana.There was no variation in acidity among the 26 accessions (Table 3).
Table 3. Means of seven physical and chemical characteristics of the fruits of 26 banana accessions of the active genebank of Embrapa FRL: fruit length (cm), FRD: fruit diameter (cm), FRW: fruit weight (g), FLW: flesh weight (g); FLD: flesh diameter (cm), PTH: peel thickness (cm), FLF: flesh firmness(Lb); * significant at 5%. # Means followed by the same letter, in the columns, belong to the same group by the clustering test of Scott and Knott (1974), at 5% probability.
The mean content of total carotenoids among the 26 accessions was 3.19 mg g -1 , ranging from 0.98 mg g -1 (Tropical, tetraploid AAAB) to 8.23 mg g -1 (Jaran, diploid AA) (Table 4).Englberger et al. (2003a) quantified carotenoid levels in 21 banana accessions and found a mean of 11.13 mg g -1 , with amplitude of variation from 0.62 to 53.70 mg g -1 .Similar results were obtained by Englberger et al. (2003b) with 17 banana accessions (mean of 9.21imgig -1 ) and Amorim et al. (2009b), who obtained a mean of 4.73 mg g -1 in the analysis of 42 diploid, triploid and tetraploid banana accessions.
Teparod and an unknown AAA contained most vitamin C, with respective values of 76.83 mg 100 -1 and 54.20 mg 100 -1 .Amorim et al. (2007) observed a variation of vitamin C from 21 to 54 mg 100 -1 in diploid banana, in agreement with our results.
The dendrogram of genetic distances based on agronomic data and physicochemical fruit characteristics, obtained by the UPGMA method, is shown in Figure 1.The cophenetic value was high (r = 0.86, P <0.0001, 10,000 permutations) and appropriate, since r³0.56 is considered ideal, indicating good agreement with the values of genetic distance (Vaz Patto et al. 2004).The cluster analysis allows the conclusion of the existence of wide genetic variability among 26 banana genotypes, a positive factor for the choice of parents for hybridization.Three major groups and several subgroups were formed.Bunch weight was highest for the tetraploids Ambrosia and Calipso and hybrids type Gross Michel, which were grouped together.
Results with bananas indicate that the carotenoid content is a quantitative trait determined by the activity of multiple gene products (Davey et al. 2009).The results of this study support this statement, since the diploids 'Jaran' and 'Malbut' with highest total carotenoid contents, although classified in the same group, formed different subgroups.This allows the conclusion that the genetic control for this trait is influenced by multiple genes.In other crops, similar results were obtained (Santos andSimon 2002, 2006).
The improved diploid 028003-01 grouped together with 'Tuugia' as expected, since this genotype is one of its parents.The tetraploids with genome AAAB (Tropical, Maravilha, Porp and Ouro da Mata) were also grouped together.The tetraploid Champa Madras, the only representative of genome ABB, formed a separate group.
It was concluded that it is possible to obtain cultivars with high levels of polyphenols, flavonoids, vitamin C and carotenoids, by crossing different genotypes and selection in the progeny.Cultivars with this profile can potentially neutralize free radicals, preventing certain diseases, including some types of cancer (Vijayakumar et al. 2008).In general, wide genetic variability was detected for most agronomic, physical and chemical characteristics of the 26 banana accessions, enabling the planning of crosses for the development of cultivars with short stature, high yield (bunch weight) high carotenoid, flavonoid and/or polyphenol contents.Among the accessions, the triploids Caipira and Thap Maeo and the tetraploids Ambrósia and Calipso performed particularly well for number of fruits and bunch weight.Highest carotenoid contents were observed in the diploid genotypes Jaran and Malbut.The highest values of total flavonoid and polyphenol contents, two natural antioxidants, were found in the tetraploid Teparod.

CONCLUSIONS
In seven of the eight wheat lines used as parents, the genotypes containing loci responsible for the grain color inheritance were fully or partially characterized.Among the genotypes evaluated, Frontana and Ônix have three genes for the determination of pre-harvest sprouting resistance, and this expression only occurs when all alleles are recessive homozygous.
The red seed color is not considered solely as a full guarantee of greater pre-harvest sprouting resistance.