Doubled haploid (DH) technology facilitates rapid development of homozygous inbred lines for hybrid breeding in maize {Zea mays L.). However, the required artificial chromosome duplication step, which commonly involves toxic and costly chemicals, represents a bottleneck. Exploiting the haploids' natural fertility may enable abolishment of artificial treatments and enhance efficiency of line development. We screened haploid populations derived from U.S. Corn Belt and tropical germplasm for the proportion of fertile haploids (FP) and the number of intact seeds (IS) on selfed ears and examined the effects of environments, heterotic groups, maturity groups, and population types on FP and IS. The FP ranged from 0 to 20% under field conditions and from 0 to 70% under greenhouse conditions. Tropical elite germplasm had higher median FP and mean IS than tropical landrace accessions. The Corn Belt heterotic group Stiff Stalk had higher niedian FP than lodent and Lancaster while early germplasm showed higher median FP than the other maturity groups. Significant (p > 0.01) genetic variance for FP was observed among elite Corn Belt materials and heritability was 0.79, indicating that recurrent selection to increase FP is promising. We propose that artificial chromosome duplication is not necessary for DH line production from germplasm with high FP. This seems particularly relevant to enable small maize breeding programs in developing countries to adopt the DH technology for line development.

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Nuclear genome size variation was studied in eight taxa of Passiflora. Nuclear DNA content was estimated by flow cytometry of nuclei stained by propidium iodide. 2C DNA content ranged from 3.16-5.36 pg for diploids and 1.83 pg for tetraploid. Differences in nuclear genome size were observed among Passiflora species (pg): P. suberosa 1.83, P. edulis f. edulis 3.16, P. edulis f. flavicarpa (Brazil) 3.19, P. edulis f. flavicarpa (Mexico) 3.21, P. mucronata 3.40, Passiflora edmundoi 3.43, P. laurifolia 3.88, P. giberti 3.92, P. quadrangularis 5.36, the largest value being up to 192% greater than the smallest. The means of 2C DNA content were compared by the Tukey test, and the differences in genome size permitted the recognition of five taxa groups. The result was the same for the means 2C genome size (Mbp) values. The genetic parameters were studied with their respective estimators, phenotypic variance (sigma2F), genotypic variability (PhiG), and the genotypic determination index (H2). The genotypic determination index presented high magnitude estimates (greater than 99%) emphasizing the reliability of the results and demonstrating the efficiency of determining the DNA content in the species using only one leaf per plant. Passiflora species show great phenotypic variability and have different geographic distribution that might implicate in genetic diversity.