The objective of this study was to test if the response to 10 cycles of a recurrent selection program conducted under conventional tillage and rain fed conditions was the same when contrasted, for several traits, under conventional and non-tillage practices. During two season (2011 and 2012) the 44 S-derived families (four/C0 to C10 populations) were evaluated under conventional and non-tillage systems in two fields next to each other. Days to anthesis, plant height, grain, and biomass yield and 1000-grain weight were determined. The grain number per m2 and harvest index was also estimated. From a random sample of 10 tillers the spikelet per spike and grains per spike were measured. For each trait, a linear mixed model (regression) was fitted to the experimental data. The slopes, under conventional tillage, were significant greater than zero for grain yield, harvest index, seeds per square meter, spikelet per spike and seeds per spike. Under non-tillage the list of traits showing slopes significantly greater than zero was shorter. For most traits there was a significant difference in the intercept terms between conventional tillage and non-tillage, which is interpreted as the tillage-practice effect. The concurrent evaluation in conventional and non-tillage soil managements of ten cycles of a recurrent selection program performed under conventional tillage confirmed the occurrence of a significant genetic progress only under conventional tillage.
Authors:A.O. Kolawole, A. Menkir, E. Blay, K. Ofori, and J.G. Kling
Two improved tropical maize composites, TZL COMP3 and TZL COMP4; representing complementary heterotic pools have been subjected to four cycles of reciprocal recurrent selection (RRS) for two decades to enhance varietal cross performance. The objectives of this study were to evaluate the effect of selection on genetic gain in heterosis for grain yield and other agronomic traits of these composites. Ten parental populations representing the C0 to C4 of each composite and their crosses plus a varietal check were evaluated in a trial at eight environments in Nigeria. Grain yield of the varietal crosses increased with selection by 3.1% cycle–1. Mean grain yields of the C4 × C4 varietal cross exceeded that of a popular improved reference variety by 23%. Selection also reduced anthesis-silking interval, improved ear characteristics, phenotypic appeal and resistance to foliar diseases. Mid-parent heterosis (MPH) increased from 4% at C0 × C0 to 24% at C4 × C4. The average rate of genetic gain in heterosis for grain yield in population crosses was 3.1% possibly because of presence of non-additive gene effects. The results of our study present the potential usefulness of the advanced selection cycle as sources of diverse inbred lines with improved combining ability as well as improved varietal crosses that can be multiplied and deployed in areas with limited market access.
Authors:A. Dashora, R. Sharma, E. Sastry, and D. Singh
A half diallel of nine genetically diverse varieties was made and the resulting 36 F
populations were evaluated along with the parents. The analysis of variance indicated that heterosis was significant for all the characters, except test weight. The heterosis components were also significant for most of the traits studied. The specific heterosis component accounted for more than 80% of the overall heterosis, indicating a complex type of inheritance for seed yield and its component traits. The crosses JF 29 × Local, RF 125 × JF 29 and UF (M)-1 × RF 101 exhibited significant positive heterobeltiosis for seed yield per plant. The parents RF125 and JF 29 merit attention as parents in the development of hybrids. The use of recurrent selection and the development of composites are suggested as ways to improve yielding ability in fennel.
Plant regeneration via tissue culture is becoming increasingly more common in monocots such as maize (Zea mays L.). Pollen (gametophytic) selection for resistance to aflatoxin in maize can greatly facilitate recurrent selection and the screening of germplasm for resistance at much less cost and in a shorter time than field testing. In vivo and in vitro techniques have been integrated in maize breeding programmes to obtain desirable agronomic attributes, enhance the genes responsible for them and speed up the breeding process. The efficiency of anther and tissue cultures in maize and wheat has reached the stage where they can be used in breeding programmes to some extent and many new cultivars produced by genetic manipulation have now reached the market.
Authors:Adriana Sánchez-Urdaneta, Cecilia Peña-Valdivia, Carlos Trejo, J. Aguirre R., and Elizabeth Cárdenas S.
The effect of substrate water potential (Ψ
) in root growth and proline content of maize seedlings of Tuxpeño Sequía C0 (TSC0) and Tuxpeño Sequía C8 (TSC8), sensitive and resistant to drought respectively, were evaluated. Seventy two hours old seedlings, with 5 cm root length, were maintained for 24 h in vermiculite at Ψ
between −0.03 and −2.35 MPa. Root length, fresh and dry weight, number of lateral roots and proline content were evaluated. Root enlargement of TSC0 was significantly higher than TSC8 at −0.03 MPa, but the response was opposite at low substrate Ψ
. The number of lateral roots was reduced in 23% in TSC8 at the lowest substrate Ψ
(−2.35 MPa) but it was not significantly affected in TSC0. A higher proline content was quantified in the cell division root region than in differentiation root region in both maize populations (5.64 and 6.96 μmol 100 mg
of dry weight in TSC0 and TSC8, respectively); and Ψ
between −0.65 and −2.35 MPa induced a drastic and significant increase of proline content in both populations. The statistical interaction between maize population, substrate Ψ
, and root region was highly significant (P≤0.0039) for proline content. The results demonstrated that eight cycles of recurrent selection of Tuxpeño for drought tolerance induced a reduction of the number of secondary roots and proline content in the differentiation root region, but a proline increase in the cell division region when root seedling grow under no restrictive water conditions (Ψ
=−0.03 MPa), beside recurrent selection modified root reaction to low substrate Ψ
by accumulation of dry matter and proline.