ALVES, V. M. C.

BAHIA FILHO, A. F. C.

OLIVEIRA, A. C.

PITTA, G. V. E

SANTOS, F. G.

SCHAFFERT, R. E.

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Genetic Variability in Sorghum for P Efficiency and ResponsivenessV.M.C. Alves, R.E. Schaffert",A.F.C. Bahia FO, G.V.E. Pitta,EMBRAPAlCNPMS, CP 151,35701-970Sete Lagoas, MG, Brazil;F.G. Santos and CA de Oliveira,Fellowship/CNPq/CNPMSThirty six sorghum lines were evaluated for Pefficiency and responsiveness at the NationalMaize and Sorghum Research Center of EM-BRAP AlCNPMS during the 1995/96 growing sea-son at Sete Lagoas, MG, Brazil. The experimentwas conducted on a Dark Red Latosol under sa-vanna vegetation soil at 5 and 18 ppm P (Mehlich-Iextractor). The soil was limed to raise the pH to arange between 5.5 and 6.0. Triple superphosphatewas broadcast and incorporated to reach the desiredP levels as determined by an incubation curve. Nand K were applied based on the soi! analysis. The36 lines included 12 traditionallines representingboth tolerance and susceptibility to AI toxicity and24lines derived from crosses between elite B-linesand a source oftolerance to AI toxicity, SC 283-liE (IS7173C). Twelve lines were susceptible totoxic levels of AI and 24 lines were tolerant. Toxiclevels of AI did not occur in the plow layer but werepresent in the subsoil. Genotypes with above aver-age grain production at the low P leveI were elas-sified as P-efficient and genotypes with above av-erage relative response to P were c1assified as re-sponsive to P. Average grain yield ranged from1.76 to 3.52 tlha at low P with a mean of2.63 tlhaand from 1.84 to 5.39 tlha at high P with a mean of3.68 tlha. The relative response to applied P rangedfrom less than zero to 93% with an average of 41%.The 36 entries were c1assified into four groups,efficient and responsive to P (ER), nonefficient andresponsive to P (NR), efficient and not responsiveto P (EN), and nonefficient and not responsive to P(NN). Tolerance and susceptibility to AI toxicitywas not directly related to P efficiency and P re-sponsiveness. The standard for tolerance to AI tox-icity, SC 283-li E, was near average for P effi-ciency (2.70 tlha at low P) and not responsive toadditional P (12%), whereas the standard for sus-ceptibility to AI toxicity, the commercial male ster-ile line BR 007B, was near average for P efficiency(2.60 tlha at low P) and highly responsive to addi-tional P (93%). The Al-tolerant line of a P-nonefficient near-isogenic pair for AI toxicity wasmore responsive to P (70%), whereas the AI sus-ceptible line of the pair was less responsive to P(33%). Two AI tolerant near-isogenic recombinantlines from the cross between BR 007 and SC 283-li E were near average for P efficiency and highlyresponsive to P (60 and 90%).Identification and Characterization ofthe MaS and Ma6 Maturity Loci in Sorghum.S. Aydin*, W.L. Rooney and F.R. Miller,Departrnent of Soil and Crop Sciences,Texas A&M University, ColIege Station, TexasThe genetics of maturity in sorghum have beenwelI documented for many years, and it has becomea model for research conceming the factors thataffect maturity or photoperiodic response in tropi-cal cereaIs. Since Quinby' (1974) first identifiedand characterized the Ma I»Ma2, Maj, and Ma410ciin sorghum, maturity in sorghum has been definedby the alIeles at those loci and their interaction.Recently, an extremely photoperiod-sensitive hy-brid was discovered from the cross of 90Tl90 andRTx430. When planted in early April, hybrids fromthis cross are extremely photoperiod-sensitive andthey will not flower until mid-October (up to 180days in Central Texas). This "ultralate" phenotypeis not caused by known combination of alIeles atthe four Ma loci currently characterized. The ob-jective ofthis research was to determine the geneticinheritance ofthis ultralate (photoperiod-sensitive)641

Genetic variability in sorghum for P efficiency and responsiveness.

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