José Branco de Miranda Filho

Estudo da capacidade combinatória de variedades de milho no esquema de cruzamento dialélico parcial

Hybrids of maize (Zea mays L.) were obtained between two variety groups, where Group 1 was made of six populations: Taiuba, Taitinga, Iubata, Moroti, Porangatu e WP12, and Group 2 was made of seven populations: Philippine DMR 2, Suwan 2, Caripeno DMR, Amarillo Dentado DMR, Cupurico DMR, Tuxpeno Crema 1 e Tuxpeno Amarillo. The performance of these populations was evaluated in the partial diallel mating scheme proposed by MIRANDA FILHO and GERALDI (1984) for plant height, ear height, ear length, ear diameter and grain weight, at Anhembi city, State of Sao Paulo, Brazil, with four replications. Structural traits were significantly different between and within the variety groups, as well as between hybrids. However, yield traits were significantly different only between variety groups and between hybrids. Significant differences were also observed between hybrids and parents, and the control did not differ from parents and hybrid average for yield. The results obtained for plant height, ear height and ear diameter did not show heterosis effects, and, for ear length, the average heterosis was 3.10%. Specific combining ability was not important and the hybrids showed an average yield of about 7% higher than their parents. Some varieties and hybrids presented a grain yield higher than the control, which was an hybrid (G-85) recommended for Southeast and Midwest Brazilian regions.

Rapid screening for aluminum tolerance in maize (Zea mays L.)

A significant decrease in maize grain yield due to aluminum toxicity is considered to be one of the most important agricultural problems for tropical regions. Genetic improvement is a useful approach to increase maize yield in acid soils, but this requires a rapid and reliable method to discriminate between genotypes. In our work we investigated the feasibility of using hematoxylin staining (HS) to detect Al-tolerant plants at the seedling stage. The original population along with two populations obtained after one cycle of divergent selection were evaluated by net root growth (NRG) and HS after 7 days in nutrient solution. Results showed a negative correlation between NRG and HS in all populations, in which sensitive plants, characterized by low NRG, exhibited more intense staining than tolerant plants. These results indicate that HS is a useful procedure for selecting Al-tolerant maize seedlings.

Heterosis expression in crosses between maize populations: ear yield

The phenomenon of heterosis has been exploited extensively in maize (Zea mays L.) breeding. The objective of this study was to evaluate the genetic potential of ten maize populations for ear yield following the diallel mating scheme. Six parental populations were obtained through phenotypic selection of open-pollinated ears in Rio Verde, GO, Brazil, (GO populations) and four parental populations were synthesized in Piracicaba, SP, Brazil (GN populations): GO-D (DENTADO), GO- F (FLINT), GO-A (AMARELO), GO-B (BRANCO), GO-L (LONGO), GO-G (GROSSO), GN-01, GN-02, GN-03 and GN-04. Experiments were carried out in three environments: Anhembi (SP) and Rio Verde (GO) in 1998/99 (normal season crop) and Piracicaba (SP) in 1999 (off-season crop). All experiments were in completely randomized blocks with six replications. Analysis of variance grouped over environments showed high significance for heterosis and its components, although mid-parent heterosis and average heterosis were of low expression. The interaction treatments x environments was not significant. Total mid-parent heterosis effects ranged from de -4.3% to 17.3% with an average heterosis of 3.37%. Population with the highest yield (7.4 t ha-1) and with the highest effect of population (vi = 0.746) was GN-03, while the highest yielding cross was GO-B x GN-03 with 7,567 t ha-1. The highest specific heterosis effect (sii = 0.547) was observed in the cross GO-B x GN-03.

Potencial da população de milho ESA23B para o melhoramento dos teores de proteína e óleo

Among the traits that may add commercial value to maize (Zea mays L.), those related to nutritional quality, specially protein and oil content, are of great interest to the feed industry. The objective of this work was studying the variability of protein and oil content, as well as yield, in a group of maize testcrosses. One hundred and twenty S1 families of the ESA23B maize population were crossed with two testers, an open-pollinated population (BR108) and an exotic line (CML269). Testcrosses were evaluated at two locations under a completely randomized block design with three replications. Ear and grain yield, protein and oil content were evaluated. The three-way interaction location x tester x progeny was significant for all traits, except for oil content. Differences among progenies were detected for all traits. Testcross means varied from 8.40% to 11.82% for protein content and from 3.77% to 5.10% for oil content. Hybrids with similar or superior means to the best check were identified for protein content, ear yield, and grain yield. Estimates of the interpopulation additive variance ranged from 0.553 to 1.124 for protein content; 0.034 to 0.057 for oil content (percent data); 132.13 to 521.74 for ear yield and 116.33 to 381.73 for grain yield (data in grams per plant). The population ESA23B can potentially be improved for all the traits studied. Associations among traits were weak, thus concomitant selection of quality and yield can be feasible.

Genetic correlation between traits in the ESALQ-PB1 maize population divergently selected for tassel size and ear height

Full-sib and selfed (S1) progenies were obtained from sub-populations of ESALQ-PB1, divergently selected for tassel size (T+ and T-) and ear height (E+ and E-), and used for estimating genetic and phenotypic correlation coefficients between traits. The analyzed traits were: EW- total ear weight (g/plant), PH- plant height (cm), EH- ear height (cm), TB- tassel branch number and TL- tassel length. The highest genetic (rG) and phenotypic (rF) correlation was observed for the combination PH x EH, as expected, with average of 0.800 and 0.778, respectively over sub-populations and locations. It is apparent that divergent selection for tassel size did not affect greatly the correlation between PH and EH in the full sib progenies, but in the inbred progenies the correlation was smaller in the sub-population selected for larger tassels. Genetic correlation between PH and EH with tassel traits was always positive but ranged from 0.020 to 0.668 in Piracicaba and from 0.06 to 0.309 in Rio Verde. Genetic correlation between PH and EH with yield (EW) also was positive in the range of 0.087 to 0.503. EH showed higher correlation with EW in relation to PH x EW and differences were larger in the sub-populations divergently selected for ear height. Correlation between tassel traits with other traits was positive in most of instances and a lack of consistency was observed among sub-populations. Generally the coefficients of genetic and phenotypic correlation differed substantially from the estimates in the base population ESALQ-PB1 before divergent selection for tassel size and ear placement. Divergent selection affected the correlation between traits under unpredicted and varying magnitudes.

Quantitative variation in the tropical maize population, ESALQ-PB1

A boa produtividade e os valores intermediarios para altura da planta e altura da espiga caracterizam a populacao de milho ESALQ-PB1 como agronomicamente promissora. Sao relatadas estimativas de parâmetros para 13 caracteres: altura da planta (PH), altura da espiga (EH), posicao relativa da espiga (EP), comprimento do pendao (TL), peso do pendao (TW), numero de ramificacoes do pendao (TB), peso de espigas (EW), peso de graos (GW), comprimento da espiga (EL), diâmetro da espiga (ED), numero de fileiras de graos (RN), numero de graos por fileira (KR) e prolificidade (PR). Os resultados se referem a um unico ambiente (um local e um ano). Foi detectada variacao genetica para todos os caracteres, e sao apresentadas estimativas da variância genetica aditiva. Os coeficientes de herdabilidade (individuos) variaram de 0,14 a 0,72 e foram considerados altos para PH, EH e TB; intermediarios para EP, TL, TW, EL e ED, e baixos para EW, GW, KR e PR. O coeficiente de herdabilidade para medias de progenies mostrou aproximadamente a mesma tendencia, variando de 0,40 a 0,75. O maior ganho esperado por selecao foi para TB (27% por ciclo) sob selecao massal e para TW (16,4%) por selecao entre progenies; o menor ganho esperado foi para ED, tanto por selecao massal (1,9%) como por selecao entre progenies (2,9%). Coeficientes de correlacao aditiva (rA) 0.5<rA<0.6 foram observados para PH ou EH e para os caracteres de producao (EW e GW) e seus componentes EL e KR, e 0,10<rA<0,44 para PH ou EH e caracteres do pendao. Para os caracteres do pendao a maior correlacao foi rA = 0,63 (TB.TW). EP foi correlacionada positivamente com TB, TW, PH, EH e PR; e negativamente correlacionada com ED e RN. As respostas correlacionadas esperadas em diversos caracteres apos selecao para GW, EH e TB sao apresentadas.

Partial diallel cross between exotic and adapted maize populations evaluated in acid soil

In Brazil, acid soils represent a large portion of the agricultural area and the development of cultivars with tolerance to acidity has shown to be feasible. The identification of germoplasm potentially tolerant to acidity was the purpose of this work. Two distinct groups of maize (Zea mays L.) populations were crossed according to the partial diallel mating scheme: Group [1] with six adapted populations and Group [2] with seven exotic varieties. All varieties and crosses were evaluated under the condition of acid and low fertility soil. Traits analyzed were: EY- ear yield, PH- plant height and EH- ear height. Outstanding varieties per se, with yield higher than 3 t ha-1, were SUWAN-2, TAITINGA, TAIUBA and IUBATA in Group [1]; and CUPURICO DMR, TUXPENO AMARILLO, and AMARILLO DENTADO in Group [2]. Heterosis and its components showed no significant variation for PH and EH; and only average heterosis was significant for EY. The general combining ability effects (gi and gj) showed significant variation (P<0.01) for all traits and were due mainly to the variation of variety effects. The higher estimates gi for EY were exhibited by WP 12 (0.178 t ha-1), TAIUBA (0.176) and TAITINGA (0.161) in Group [1]; and for gj by CUPURICO DMR (0.300), TAITINGA TUXPENO AMARILLO (0.280) in Group [2], respectively. The variety cross TAITINGA x TUXPENO AMARILLO with mean yield of 4.34 t ha-1 and 25% of mid-parent heterosis may be indicated as an heterotic pattern. PH and EH were not considered as limiting to preclude the use of the outstanding populations. The varieties SUWAN 2, CUPURICO DMR, and TAITINGA were suggested to be used in maize breeding programs for acid soils.

The partial circulant diallel cross at the interpopulation level

The partial circulant diallel cross mating scheme of Kempthorne and Curnow (Biometrics 17: 229-250, 1961) was adapted for the evaluation of genotypes in crosses at the interpopulation level. Considering a random sample of n lines from base population I, and that each line is crossed with s lines from opposite population II, there will be ns sampled crosses that are evaluated experimentally. The means of the ns sampled crosses and the remaining n(n - s) crosses can be predicted by the reduced model where Yij is the mean of the cross between line i (i = 1,2,...,n) of population I and line j (j = 1,2,...,n) of population II; µ is the general mean, and gi and gj refer to general combining ability effects of lines from populations I and II, respectively. Specific combining ability (Sij) is estimated by the difference . The sequence of crosses for each line (i) is [i x j], [i x (j + 1)], [i x (j + 2)], ..., [i x (j + s -1)], starting with i = j = 1 for convenience. Any j + s -1 > n is reduced by subtracting n. A prediction procedure is suggested by changing gi and gj by the contrasts i = i. - .. and j = .j - ..; the correlation coefficient (r) was used to compare the efficiency of s and s for selection of lines and crosses. The analysis of variance is performed with the complete model Yij = µ + gi + gj + sij + ij, and the sum of squares due to general combining ability is considered for each population separately. An alternative analysis of variance is proposed for estimation of the variance components at the interpopulation level. An analysis of ear length of maize in a partial diallel cross with n = 10 and s = 3 was used for illustration. For the 30 interpopulation crosses analyzed the coefficient of determination (R2), involving observed and estimated hybrid means, was high for the reduced (g) model [R2 (ij, Yij) = 0.960] and smaller for the simplified () model [R2 (ij, Yij) = 0.889]. Results indicated that the proposed procedure may furnish reliable estimates of means of hybrids not available in the partial diallel.

Quantitative variation for grain quality in Brazilian maize populations

Development of maize (Zea mays L.) cultivars with high grain protein and oil concentrations and an appropriate amino acid composition, without losses in grain yield, represents a challenge in breeding programs. The objective of this work was to study the nutritional quality of ten Brazilian maize populations evaluated in three environments. A randomized block design with six replications was used. Ear yield and the concentrations of protein, oil, serine, glutamic acid, alanine, leucine, tyrosine and phenylalanine were evaluated. Individual and combined analyses of variance were performed. Populations diverged for most of the traits. Environmental effects influenced variation for most of the traits, unlike genotype-environment interaction, allowing the selection on the average of environments. Positive association exists among protein and most of the amino acids, when considered on a dry matter basis and there is no association between nutritional quality and yield; therefore, the development of cultivars that are superior for both traits is expected to be feasible.

Inbreeding in two maize subpopulations selected for tassel size

O presente trabalho foi baseado na avaliacao de progenies de irmaos germanos e S1 da populacao de milho (Zea mays L.) ESALQ-PB1 depois de seis ciclos de selecao divergente para tamanho do pendao. Os seguintes caracteres foram analisados: altura da planta, altura da espiga, numero de ramificacoes do pendao, comprimento do pendao e peso do pendao. Para todos os caracteres, as unidades experimentais foram medias de tres plantas por parcela. As progenies foram avaliadas em onze experimentos (blocos completamente casualizados) com tres repeticoes em Piracicaba ¾ SP, Brasil. As medias das progenies endogâmicas (m1) e nao endogâmicas (m0) foram usadas para estimar a depressao por endogamia (I = m1 ¾ m0) e a contribuicao de homozigotos (m0 + a*) e heterozigotos (d*) para a media populacional. Considerando os cinco caracteres sob estudo, a depressao por endogamia variou de 1,9 to 15,9% mas somente para altura da planta foi detectada significância para aquele efeito. Os caracteres da planta exibiram maior depressao do que os caracteres do pendao; e o numero de ramificacoes do pendao parece ser mais sensivel a endogamia do que os outros caracteres do pendao. Com excecao de altura da planta, foi evidente que a depressao por endogamia foi maior na subpopulacao selecionada negativamente para tamanho do pendao (T¾). As estimativas de A = m0 + a* e d* indicam um menor efeito dos desvios de dominância para todos os caracteres, quando comparados com a contribuicao dos homozigotos. Foi detectada variabilidade significativa entre progenies na maioria dos casos.