Effectiveness of selection, parent-offspring correlation and regression in bacterial blight resistance genes introgressed rice segregating population

Abstract

The effectiveness of early generation selection was practiced in bacterial blight resistance genes introgressed F₂ and F_2:3 population of the cross CB 174 R × IRBB 60 in rice. F₂ Selection have been proved to be robust and effective tool in crop improvement program. Selection differential was positive for all studied traits. Selection response was high for number of grains, thus indicating the effectiveness of selection for these character. Realized heritability was found high for number of grains and thousand grain weight, suggested that direct selection was effective. Expected selection response and predicted genetic gain was high for number of grains. Parent-offspring correlation showed low but significance association for number of productive tillers (r=0.47^**, P<0.01), single plant yield (r=0.35^**, P<0.01) and (r=0.30^*, P<0.05) panicle length in F₂ and F_2:3 generation indicates that selection was fruitful in early generation. Statistically regression coefficient was not significant linear dependence of the mean of F₂ and F_2:3 generation.

Alternate abstract:

A eficácia da selecção das primeiras gerações foi praticada na população F2 e F2: 3 de CB 174 R × IRBB 60 do gene bacteriano. A seleção foi positiva para todos os caracteres estudados. A resposta de seleção foi alta para o número de grãos. A herdabilidade realizada foi encontrada alta para o número de grãos e mil grãos de peso, sugeriu que a seleção direta foi eficaz. A resposta à seleção esperada e o ganho genético previsto foi elevado para o número de grãos. A correlação entre pais e filhos mostrou forte associação com o número de latifundiários produtivos (r = 0,47^**, P<0,01), produção única de planta (r = 0,35^**, P<0,01) e (r = 0,30^*, P<0,05) Comprimento em F2 e F_2:3 geração indica que a seleção foi frutífera. O coeficiente de regressão estatística não foi dependência linear significativa da média de F2 e F_2:3 geração.

INTRODUCTION:

Rice (Oryza sativa L.) is a major food crop in India and the estimated total rice production was 103.61 million tones during 2015-16, which was 1.87 million tones lower as compared to the year 2014-15 production (105.48 million tones) (^{Agricultural situation in India, 2016}). Bacterial blight (BB) is caused by Xanthomonas oryzae pv. oryzae (Xoo) and could be identified by two symptoms on rice; kresek and leaf blight. Kresek is the more destructive manifestation of the disease. Leaves of entire plants turn pale yellow and wilt during the seedling to early tillering stages. Leaf blight is the more common disease, in which the lesions on the leaf blades may extend to the leaf sheath. Lesion enlarges in length and width, and may have wavy margins. BB disease of rice, in terms of yield losses across the globe (^{DAS et al., 2014}) and yield losses up to 80% depending on the stage of the crop, cultivar susceptibility, and environmental conditions (^{SRINIVASAN & GNANAMANICKAM, 2005}). For increasing the yield potential, hybrids are considered as an important strategy in any crop. Even though, hybrids are performing well for yield and quality, but susceptible to biotic stress like bacterial blight which reduces yield. Gene pyramiding is a very useful approach to maximize utilization of existing gene resources. Pyramiding multiple resistance genes into an existing variety proves to be an effective approach for achieving broad-spectrum and durable resistance in rice (^{CHEN et al., 2009}). Incorporation of resistance genes into both parents of hybrid is necessary for expression of desired level of resistance. Among the segregating populations F₂ generation is most crucial, where selection has to be done more critically. Segregating populations would allow the gene expression for particular traits. Effectiveness of early generation selection was studied by many researchers in wheat through correlations between F₂ and F₃ (^{PAWAR et al., 1989}) and between F₂ and F₃ and F₃ and F₄ (^{SAINI & GAUTAM, 1990}). Estimates of realized heritability of the particular trait is important in determining its response to yield and its components has been reported by some workers in rice (^{KATO, 1997}; ^{TAKEDA & SAITO, 1983}; ^{GRAVOIS & MCNEW, 1993}). Selection pressure in rice based on grain yield, total tillers and grain per panicle could be advantageous (^{TALWAR, 1976}). Effectiveness of early generation selection could be reduced by genotype and environment interaction (^{WHAN et al., 1981}; ^{RAHMAN & BAHL, 1986}). Direct selection may not be effective in segregating population for improvement of grain yield (^{BARTLEY & WEBER, 1952}; ^{JOHNSON et al., 1955}). Parent offspring correlation and regression between two generations shows lesser influence of environment and it’s very useful method for selection in segregating population. Therefore, present study aimed to know agronomical performances of the bacterial blight resistance genes introgressed individuals with subsequent generations and thus will help to improve breeding efficiency.

MATERIALS AND METHODS:

Plant materials

The experimental materials were consisted of F₂ population obtained from F₁ cross of CB 174 R × IRBB 60. CB 174 R is the restorer parental line of released rice hybrid CORH 4 (COMS 23A/CB 174 R) in TNAU, having the features of medium slender grain type and matures in 135 days. IRBB 60 is a donor parent for bacterial blight resistant, carrying the genes of Xa21, xa13 and xa5 on chromosome 11, 8 and 5, respectively. An experiment was conducted at Department of Rice, Tamil Nadu Agricultural University, Coimbatore. Three/two genes introgressed F₂ individuals were identified and advanced to obtain F_2:3 population based on gene specific SSRs genotyping. Finally, fifty four plants were selected and selfed to make F_2:3 families and nine plants from each F_2:3 families were evaluated. The standard agronomical practices were followed through the season to grow healthy crop.

Traits measured

Data was collected on individual plants in F₂ and nine plants were in each F_2:3 families at or after physiological maturity on the basis of single plant. Traits were included plant height (cm, from the ground level to the tip of the primary panicle of selected plants at the time of maturity), number of productive tillers (panicle bearing tillers counted), panicle length (cm, length of the panicle on the main axis measured at the grain maturity stage), number of grains (dry threshed grain per plant used to count by seed counter), thousand grain weight (g, weight of the dry threshed 1000 grain per plant) and single plant yield (g, weight of the dry threshed grain per plant).

Data analysis

Experimental data on aforesaid traits were subjected to selection differential and response to selection were worked out as suggested by ^{SINGH & SINGH, (1994}), while realized heritability was estimated as per ^{FALCONER & MACKAY, (1996}). The expected response to selection expressed as % of the base population mean (% RS) and the expected genetic gain (PGG) were calculated using the formulas reported by ^{CRUZ et al. (2012}). Parent-offspring regression was calculated using GraphPad Prism 5.0 (GraphPad Software, Inc., San Diego, CA), early generation evaluation was also done by parent-offspring correlation between F₂ selections and with their progenies in F_2:3 using Microsoft excel 2007 (Microsoft Crop., Redmond, WA, USA).

RESULTS AND DISCUSSION:

Based on individual plant performances for disease resistance, yield and five other traits which were component of yield performance of 54 F₂ plants were selected and evaluated in F_2:3 generation. Heritability mainly studied to determine how much variation in the phenotype in a population is due to genetic variation between individuals in that population. To develop superior cultivar, there should be high mean values with adequate genetic variability it could be achieved in segregating populations like F₂ and F_3. Higher estimate of realized heritability was reported in number of grains and thousand grain weight, which indicated that selection was effective in F₂ population. Similar findings were also reported that selection for heritable characters like thousand grain weight was effective in early generation in rice (^{SUN, 1979}; SUB^{RAHMANYAM et al., 1986}; ^{SUREK & BESER, 2005}; ^{KUMAR et al., 2009}). Relatively low realized heritabilities were observed in plant height, panicle length, number of productive tillers and single plant yield in F₂ generation. Of these traits, plant height (^{TORIYAMA & FUTSUHARA, 1958}; ^{YAMAMOTO & TORIYAMA, 1971}) and panicle length showed lower heritability compared with other traits. Most of the studied characters in F₂ generation showed negative direction in selection response and realized heritability. Although, observed realized responses for these two traits in this cross which might be explained by genotypic differences between their parents and were utilized in breeding programme. Similar results were previously reported by ^{MISHRA et al. (1993}). The present study showed that selection differential was positive value for the studied traits except for thousand grain weight in F₂. This finding was concluded that genetic drift and inbreeding was low in F₂ population (^{FALCONER & MACKAY, 1996}). Highest and positive realized heritability was reported between F₂ generation for number of grains (^{KATO, 1997}). Single plant yield (r=0.35^**, P<0.01) exhibited positively significant correlation coefficients between F₂ and F_2:3, indicating that strong associations between this trait. Similar kinds of results were reported by ^{DHANRAJ et al. (1987}), ^{JANGALE et al. (1987}), KUMAR et al. (2009), ^{BARMAN & BORAH (2012}) for grain yield. Some of researchers emphasized the use of early testing in F₂ and subsequent generations for yield (^{SNEEP, 1977}; ^{COOPER, 1981}). ^{SHEBESHKI (1967}) suggested that for the identification of superior gene combinations even in the heterozygote, certainly some point of view the proportion of the plants with most desirable gene combination decreases rapidly with the advancement of generations and if these were not selected in the early generations even if heterozygote condition, these would be lost. The present results get supported with the suggestion of SHEBESHKI (1967) as higher number of superior alleles governed individuals were recovered when early selection in F₂ was practiced. Statistically regression coefficient was not significant linear dependence of the mean of F₂ and F₂:₃ generation (Table 1 and 2, Figure 1). This finding might be the reason of accumulating two or three genes introgressed F₂ and F_2:3 individuals were used (either homozygous or heterozygous state) and it will segregate in F_2:3 families and, it should need to be studied further.

Table 1 Estimates of selection parameters in F₂ and F_2:3 progenies for yield and its component traits in the cross CB 174R × IRBB 60.

Note: PH: Plant height (cm), NPT: Number of productive tillers, PL: Panicle length (cm), NG: Number of grains per panicle, 1000GW: Thousand grain weight (g), SPY: Single plant yield (g).

Table 2 Parent-offspring correlation for yield and their component traits in rice cross of CB 174 R × IRBB 60.

^*,^**significant at P<0.05 and P<0.01, respectively. Note: PH: Plant height (cm), NPT: Number of productive tillers, PL: Panicle length (cm), NG: Number of grains per panicle, 1000GW: Thousand grain weight (g), SPY: Single plant yield (g).

[Image Omitted: See PDF]

CONCLUSION:

Present study confirmed that thus usefulness of selection in early generation and it may have greater impact on breeding program of rice with respect to thousand grain weight and single plant yield. Parent-offspring correlation showed strong association for number of productive tillers, single plant yield and panicle length in F₂ and F_2:3 generation indicates that selection was effective at this stage.

E-mail:[email protected]. * Corresponding author.

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