The objective of this study was to estimate genetic parameters and quantify the correlations between late blight (LB) resistance and fruit quality traits in 220 families F2:3, under tropical field conditions. The families were arranged in randomized blocks in field trials, with six resistant inbred lines used as control, in plots of five plants. It evaluated the severity in the middle of the epidemy, final severity, area under the curve of progress of late blight, pH, total soluble solids, titratable acidity and flavor. There is genetic variability for epidemiological variables and total soluble solids. Heritabilities, obtained by parent-offspring regression, were high and indicated the possibility of satisfactory genetics gains and success in the introgression of resistance alleles. The correlations were negative, of high to intermediate magnitude, among the variables area under the curve of progress of late blight, total soluble solids and total titratable acidity.
Late blight (LB) caused by the oomycete Phytophthora infestans (Mont.) de Bary, is the most destructive disease in the cultivated tomato, Solanum lycopersicum L. [
Cultivars with genetic resistance are a desirable alternative in reducing the environmental and economic fungicide spray coast [
This phenomenon occurs when chromosome segments containing alleles of interest are linked to loci that contain deleterious alleles from the horticultural traits [
In order to elucidate the association between LB resistance traits and fruit quality, the objective of this study was to estimate genetic statistical parameters and correlations in 220 F2:3 Solanum habrochaites f. glabratum progenies.
The susceptible cultivar “Santa Clara”, S. lycopersicum L., was used as female genitor in crossing with BGH 6902 accession, S. habrochaites f. glabratum, LB resistant. The female genitor belongs to the “Santa Cruz” brazilian fresh market tomato group, it has bi or triloculars oblong fruits, consumed in natura and fruits weight 130 g in average. Male genitor is a wild specie kept on the Banco de Germoplasma de Hortaliças da Universidade Federal de Viçosa (BGH/UFV—www.bgh.ufv.br) and produce small greenish fruits with unpleasant taste and odor. Part of the F1 plants was self-pollinated for the obtantion of F2 generation, which originated 220 F2:3.
The experiments were carried out at the experimental area of the Universidade Federal de Viçosa (UFV), in Viçosa, MG State, Brazil, located in the latitude 20˚45'14''S, longitude 42˚52'53''W and 648.74 m high.
In 2010 it was evaluated 220 F2:3 families for LB resistance, divided in two trials, both in randomized blocks with two repetitions and six common controls in each trial: the lines 127f, 64b, 73d e 133a [
The growing methods followed the instructions of [
P. infestans isolates pathogenic to tomato, from the towns of Cajuri, Coimbra, Teixeiras and Viçosa, located at Zona da Mata Mineira, Minas Gerais state, were used for the inoculums preparation, according metology [
Infected leaflets were collected and kept in plastic trays previously disinfected in 70% alcohol, lined with paper towels moistened in distilled water and kept at 18˚C for 24 h for incubation. After the incubation period, foliar lesions with mycelium and sporangia were removed and placed in flasks with distilled water. Subsequently, the mixture was stirred in an agitator to form a sporangia suspension. The concentration of the suspensions was adjusted by hemacytometer to 5 × 103 sporangia per mL. Then, equal volumes from four locals were mixed. The sporangia suspension was placed in refrigerator for 1 h, at a temperature of about 4˚C, to induce zoospores release.
Inoculation of seedlings occurred 50 days after transplanting in the field. The inoculation was done at the dusk with backpack sprayer, applying approximately 10 mL of the suspension per plant. The period from the inoculums preparation to inoculation was less than 2 h, avoiding unfeasibility of zoospores. The plants were watered at dusk by sprinkling for 2 h three times a week until the end of the experiment.
The fruit quality traits, total acidity (pH); total soluble solids (˚Brix), measured with a portable refractometer, total titrable acidity (% citric acid) and flavor, obtained by the ratio of total soluble solids and total titrable acidity, were measured using samples of five fruits picked on the second and third cluster. These analyses were performed according to the analytical standard proposed by the [
The disease was quantified by the percentage of the disease severity (DS) in intervals of three days, for 15 days [
The DS were subsequently used to estimate the area under the disease progress curve (AUDPC), and the other epidemiological traits: severity on the middle of the epidemy (Y50) and final severity (YMax). It was considered, as the duration of the epidemy, the time between the first and the last evaluation. The phenotypic values of each family were obtained by the average of the grades attributed to the leaves of the three central plants of each plot.
The analysis of variance were conducted using the joint analysis for the group of experiments, which were analyzed together with the common (controls) and non common (families) treatments, so that the comparison between then were done indistinctly of the trial where they were evaluated. This procedure was used in function of the great number of families, and it was used the first scheme, according to the methodology proposed by [
The statistical and genetic parameters estimated were: the experimental coefficient of variation, genetic coef- ficient of variation, ratio between the genetic variation coefficient and environmental variation, the component of genetic variance, heritability in a broad sense in level of the averages of F2:3 families, heritability parent- offspring and the phenotypic, genotypic and environmental correlation between the epidemiological variables and fruit quality attributes.
The parent-offspring heritability for the phenotypic variables, Y50, YMAX and area under the curve of progress of late blight was obtained according to the methodology proposed by Smith and Kinman (1965), described by [
The joint analysis of variance showed not to be significant the interaction between controls vs. trials for the traits evaluated. Coefficients of experimental variation of high values were estimated for Y50, YMAX and AUDPC (
Because it is an average value between two trials, high estimates can be due to climatic differences between the periods of evaluation of severity in each trial. However, the values are similar to the ones found by [
The estimates of the parameters, coefficient of genetic variation, ratio between coefficient of genetic variation/experimental and heritability, are of great value for the breeding, once they are also used on the quantification of the available genetic variability. The coefficient of genetic variation, CVg, gives an idea about the proportionality of the gain in relation to the average in case of selection, and the ration CVg/CVe > 1 indicates favorable situation to selection [
The heritability shows how much of the phenotypic variation is due to the genetic effects. So, if the values of heritability are high, there is a high correlation between the phenotypic and genotypic value, so that the meas-
. Summary of the joint analysis of variance of 220 families F2:3 derived from the cross between Solanum lycopersicum and Solanum habrochaites f. glabratum evaluated for epidemiological and fruit quality, together with six commons controls in both trials
SV | DF | Mean squares | ||||||
---|---|---|---|---|---|---|---|---|
Y50 | YMAX | AUDPC | pH | ˚Brix | TTA | Flavor | ||
Blocks/trials | 2 | 5216.49 | 15484.60 | 951751.97 | 0.63 | 3.99 | 0.0049 | 161.51 |
Trials | 1 | 2829.61 | 16998.59 | 17108.59 | 0.43 | 0.56 | 0.0117 | 510.86 |
Control | 5 | 447.17 | 1078.40 | 73612.10 | 0.06 | 0.80 | 0.0050 | 76.52 |
Control × trials | 5 | 87.26ns | 220.77ns | 8958.10ns | 0.03ns | 0.43ns | 0.0007ns | 11.46ns |
Families | 218 | 165.77* | 374.77* | 23057.94* | 0.20ns | 1.04** | 0.0026ns | 100.19ns |
(Cont. vs. fam.)/trial. | 2 | 549.41 | 684.96 | 130542.89 | 0.11 | 2.35 | 0.0049 | 85.32 |
Residual | 230 | 90.52 | 216.89 | 10811.67 | 0.17 | 0.83 | 0.0022 | 93.41 |
Total | 463 | |||||||
General average | 18.68 | 40.10 | 280.31 | 4.19 | 3.94 | 0.15 | 27.175 | |
Families average | 18.92 | 40.34 | 284.46 | 4.19 | 3.94 | 0.15 | 27.29 | |
Control’s average | 14.29 | 35.81 | 204.28 | 4.28 | 4.06 | 0.17 | 24.86 | |
CV% | 50.90 | 36.71 | 37.09 | 10.00 | 23.09 | 30.72 | 35.56 |
* and ** significant by the F test (P < 0.01 e 0.05); Y50 = severity in the middle of the epidemy; YMAX = final severity; AUDPC = area under the curve of progress of late blight; pH = potential of hydrogen; ˚Brix = total soluble solids; TTA = total tritable acidity and flavor.
Table 2. Estimates of average genotypic variance (Vg), broad-sense heritability (), genetic coefficient of variation (CVg), experimental coefficient of variation (CVe), ratio between experimental and environmental variation (CVg/CVe), for epide- miological traits related to the resistance to late blight and fruit quality in progenies of tomato derived from the cross between Solanum lycopersicum and Solanum habrochaites f. glabratum.
Parameter | Y50 | YMax | AUDPC | pH | ˚Brix | TTA | Flavor |
---|---|---|---|---|---|---|---|
Vg | 37.62 | 78.93 | 6123.13 | 0.01 | 0.11 | 0.01 | 3.38 |
45.39 | 42.12 | 53.11 | 14.04 | 20.77 | 12.97 | 6.76 | |
CVg | 32.40 | 22.02 | 27.50 | 2.86 | 8.37 | 8.44 | 6.74 |
CVe | 50.90 | 36.71 | 37.09 | 10.00 | 23.09 | 30.72 | 35.56 |
CVg/CVe | 0.63 | 0.59 | 0.74 | 0.28 | 0.36 | 0.27 | 0.18 |
Y50 = severity in the middle of the epidemy; YMax = final severity; AUDPC = area under the curve of progress of late blight; pH = potential of hydrogen; ˚Brix = total soluble solids; e TTA = total tritable acidity; flavor: ratio between total soluble solids and total tritable acidity.
ured differences in the individuals translate the true genetic differences and guarantee thus the success of the selection strategy adopted [
The values of heritability of the fruit quality traits were low (
Regarding to the epidemiological traits, the estimates of the broad-sense heritability were lower than 50%, except for AUDPC, which estimate was 53.11% (
The heritability estimated by parent-offspring were satisfactory: 62.72% for Y50, 56.61% for YMAX and 71.20% AUDPC (
Besides the analysis of population parameters, the correlations between the phenotypic traits assist in the understanding of the genic effect of the trait of interest [
For the combination between epidemiological traits, the estimates of genetic correlation was of magnitude higher than 0.9 (
AUDPC was considered the trait that best represented the response of the progeny in relation to the resistance to the pathogen. Because of the genotypic variance, statistically null, estimated for the fruit quality attributes, it was not estimated the genetic correlation between these traits and the area under the curve of progress of late blight. The association between these traits was realized by phenotypic correlations (
. Estimates of parent-offspring heritability, Smith and Kinman (1965), of epidemiological traits related to the resistance to late blight in progenies of tomato derived from the cross between Solanum lycopersicum and Solanum habrochaites f. glabratum
Parameters | F2 average | F2:3 average | Cov (F2; F2:3) | Correlation | h2 |
---|---|---|---|---|---|
Y50 | 3.30 | 18.05 | 9.86 | 0.23 | 62.72 |
YMax | 39.89 | 52.53 | 125.12 | 0.27 | 56.51 |
AUDPC | 161.17 | 279.49 | 5418.96 | 0.48 | 71.20 |
Y50 = severity in the middle of the epidemy; YMax = final severity; and AUDPC = area under the curve of progress of late blight.
. Phenotypic (P), genotypic (G) and environmental (E) correlations between epidemiological traits related to the resistance to late blight in progenies of tomato derived from the cross between Solanum lycopersicum e Solanum habrochaites f. glabratum
Traits | Correlations | YMAX | AUDPC |
---|---|---|---|
Y50 | P | 0.63 | 0.87 |
G | 0.97 | 0.99 | |
E | 0.40 | 0.76 | |
YMax | P | - | 0.76 |
G | - | 0.92 | |
E | - | 0.63 |
Y50 = severity in the middle of the epidemy; YMax = final severity; and AUDPC = area under the curve of progress of late blight.
. Correlations between the area under the curve of progress of late blight and fruit quality attributes in progenies of tomato derived from cross between Solanum lycopersicum e Solanum habrochaites f. glabratum
Traits | pH | Brix | TTA | Flavor |
---|---|---|---|---|
AUDPC | 0.27** | −0.41** | −0.31** | 0.02 |
pH | - | 0.08 | −0.03 | 0.34** |
BRIX | - | - | 0.48** | 0.44** |
TTA | - | - | - | −0.47** |
** and * significant at 1% and 5% of probability by the t test; AUDPC = area under the curve of progress of late blight; pH = potencial of hydrogen; ˚Brix = total soluble solids; TTA = total tritable acidity; and flavor = ratio between total soluble solids and total tritable acidity.
The correlations between AUDPC, ˚Brix and ATT were significant, negative and of intermediate magnitude, indicating that alleles of resistance can contribute favorably for the organoleptic qualities of the fruits, as the ratio between the content of total soluble solids and total tritable acidity determines the flavor. The results found ratified the reports by [
These authors concluded that the alleles of S. habrochaites were responsible for an increment of 15% in the content of soluble solids, emphasizing that wild germplasms are potentially donators of alleles of agronomic interest for elite-cultivars. The content of soluble solids (˚Brix) positively correlated with total tritable acidity, agreed in magnitude and direction to the estimates obtained by [
Through the results, it appears that there is genetic variability for all traits in the population under study. However, low values of heritability of the fruit quality traits were found. The estimates of heritability by parent- spring regression were high and indicated the possibility of satisfactory gains, in addition to greater ease in the introgression of alleles of resistance. The correlations between the traits AUDPC, ˚Brix and TTA were negative and of intermediate magnitude, indicating that alleles of resistance can favorably contribute to the flavor of the fruits.
It found genetic variability for all traits. The quality attributes of fruits have low heritability, while the heritability parent-offsspring epidemiological variables were of great magnitude indicating the possibility of satisfactory earnings.
To Fundação de Amparo à Pesquisa do Estado de Minas Gerais, for financial support; to Coordenação de Aperfeiçoamento de Pessoal de Nível Superior and Conselho Nacional de Desenvolvimento Tecnológico e Cientifico, for scholarship granted. To Universidade Federal de Viçosa.