Pablo Quijada

Inbreeding depression in tropical maize populations prior and following full-sib recurrent selection Full-sib recurrent selection (FSRS) was conducted in the following six tropical maize populations: (Suwan-1, Foremaiz-2, La Maquina, Compuesto Thai-1, Tuxpeño RC and Agua Blanca). The original populations (Co), their improved cycles (Cn), and S1 generation of both original and improved populations were evaluated in five locations in Venezuela. The objective of the study was to estimate inbreeding depression of the populations, before and after FSRS. Grain yield (GY), plant height (PH), ear height (EH), and days to silk (DS) were the traits used to estimate inbreeding depression. Inbreeding resulted in a significant reduction in GY, PH and EH and a significant increase in DS. For GY and PH inbreeding depression was significantly higher for the improved than for the original populations, whereas for EH and DS inbreeding depression rate and percentage were similar in both populations. R...

Inbreeding depression in tropical maize populations prior and following full-sib recurrent selection Full-sib recurrent selection (FSRS) was conducted in the following six tropical maize populations: (Suwan-1, Foremaiz-2, La Maquina, Compuesto Thai-1, Tuxpeño RC and Agua Blanca). The original populations (Co), their improved cycles (Cn), and S1 generation of both original and improved populations were evaluated in five locations in Venezuela. The objective of the study was to estimate inbreeding depression of the populations, before and after FSRS. Grain yield (GY), plant height (PH), ear height (EH), and days to silk (DS) were the traits used to estimate inbreeding depression. Inbreeding resulted in a significant reduction in GY, PH and EH and a significant increase in DS. For GY and PH inbreeding depression was significantly higher for the improved than for the original populations, whereas for EH and DS inbreeding depression rate and percentage were similar in both populations. R...

Functional genetic redundancy is widespread in plants and could have an important impact on phenotypic diversity if the multiple gene copies act in an additive or dosage-dependent manner. We have cloned four Brassica rapa homologs (BrFLC) of the MADS-box flowering-time regulator FLC, located at the top of chromosome 5 of Arabidopsis thaliana. Relative rate tests revealed no evidence for differential rates of evolution and the ratios of nonsynonymous-to-synonymous substitutions suggest BrFLC loci are not under strong purifying selection. BrFLC1, BrFLC2, and BrFLC3 map to genomic regions that are collinear with the top of At5, consistent with a polyploid origin. BrFLC5 maps near a junction of two collinear regions to Arabidopsis, one of which includes an FLC-like gene (AGL31). However, all BrFLC sequences are more closely related to FLC than to AGL31. BrFLC1, BrFLC2, and BrFLC5 cosegregate with flowering-time loci evaluated in populations derived by backcrossing late-flowering alleles...

Functional genetic redundancy is widespread in plants and could have an important impact on phenotypic diversity if the multiple gene copies act in an additive or dosage-dependent manner. We have cloned four Brassica rapa homologs (BrFLC) of the MADS-box flowering-time regulator FLC, located at the top of chromosome 5 of Arabidopsis thaliana. Relative rate tests revealed no evidence for differential rates of evolution and the ratios of nonsynonymous-to-synonymous substitutions suggest BrFLC loci are not under strong purifying selection. BrFLC1, BrFLC2, and BrFLC3 map to genomic regions that are collinear with the top of At5, consistent with a polyploid origin. BrFLC5 maps near a junction of two collinear regions to Arabidopsis, one of which includes an FLC-like gene (AGL31). However, all BrFLC sequences are more closely related to FLC than to AGL31. BrFLC1, BrFLC2, and BrFLC5 cosegregate with flowering-time loci evaluated in populations derived by backcrossing late-flowering alleles...

Sclerotinia stem rot, caused by fungus Sclerotinia sclerotiorum, is one of the most devastating diseases in rapeseed (Brassica napus L.). We report the identification of Quantitative trait loci (QTL) involved in the resistance to S. sclerotiorum in two segregating populations of DH lines: the HUA population, derived from a cross between a partially resistant Chinese winter line (Hua dbl2) and a susceptible European spring line (P1804); and the MS population, derived from a partially resistant French winter cultivar (Major) and a susceptible Canadian spring cultivar (Stellar). A petiole inoculation technique and two scoring methods, days to wilt (DW) and stem lesion length (SLL), were used for the resistance assessment. A total of eight genomic regions affecting resistance were detected in the HUA population, with four of these regions affecting both measures of resistance. Only one region, which affected both measurements, was detected in the MS population. Individual QTL explained 6-22% of the variance. At five of the QTL from both populations, alleles from the resistant parent contributed to the resistance. QTL on N2 from the HUA population had the highest LOD score and R (2) value and was detected for SLL in the first evaluation. The N12 resistance allele in Hua dbl2 was detected in a region containing a homeologous non-reciprocal transposition (HNRT) from the resistance-containing portion of N2. This result suggests that QTL in the N12.N2 HNRT enhanced the resistance of Hua dbl2 by increasing the dosage of resistance genes. The relationship of QTL from different genetic backgrounds and their associations with other agronomic traits are discussed.

Sclerotinia stem rot, caused by fungus Sclerotinia sclerotiorum, is one of the most devastating diseases in rapeseed (Brassica napus L.). We report the identification of Quantitative trait loci (QTL) involved in the resistance to S. sclerotiorum in two segregating populations of DH lines: the HUA population, derived from a cross between a partially resistant Chinese winter line (Hua dbl2) and a susceptible European spring line (P1804); and the MS population, derived from a partially resistant French winter cultivar (Major) and a susceptible Canadian spring cultivar (Stellar). A petiole inoculation technique and two scoring methods, days to wilt (DW) and stem lesion length (SLL), were used for the resistance assessment. A total of eight genomic regions affecting resistance were detected in the HUA population, with four of these regions affecting both measures of resistance. Only one region, which affected both measurements, was detected in the MS population. Individual QTL explained 6-22% of the variance. At five of the QTL from both populations, alleles from the resistant parent contributed to the resistance. QTL on N2 from the HUA population had the highest LOD score and R (2) value and was detected for SLL in the first evaluation. The N12 resistance allele in Hua dbl2 was detected in a region containing a homeologous non-reciprocal transposition (HNRT) from the resistance-containing portion of N2. This result suggests that QTL in the N12.N2 HNRT enhanced the resistance of Hua dbl2 by increasing the dosage of resistance genes. The relationship of QTL from different genetic backgrounds and their associations with other agronomic traits are discussed.

... cultivar Reward, to an inbred B. oleracea plant, TO1000. 'Reward' is a spring canola quality cultivar with white rust [caused by Albugo candida (Pers.) Kunze] resistance (Scarth et al., 1992). TO1000, is a S 5 inbred line derived ...

... Pablo A. Quijada a ,; Joshua A. Udall b ,; Hieronim Polewicz c ,; Robert D. Vogelzang a and; ... at most other marker loci (Osborn et al., 1997; Vogelzang and Osborn, unpublished data). ... The second test was performed with the Statistical Analysis System (SAS, Cary, NC) Generalized ...