One of the critical limitations for the in vivo production of doubled haploid (DH) lines in maize (Zea mays L.) is the inability to effectively identify haploids in a significant proportion of induction crosses due to the possibility of complete or partial inhibition of the currently used R1-nj (Navajo) color marker. In this study, we demonstrate that the R1-nj marker could result in a high proportion of false positives among the haploids identified, besides being ineffective in germplasm with natural anthocyanin expression in pericarp tissue. To address these limitations, we developed haploid inducer lines with triple anthocyanin color markers, including the expression of anthocyanin coloration in the seedling roots and leaf sheaths, in addition to the Navajo marker on the seed. Although these inducers show acceptable haploid induction rates ranging from 8.6 to 10.2%, they exhibited relatively poor agronomic performance compared with tropicalized haploid inducers within tropical environments. The addition of the red root marker more accurately identified haploids among the germinating seedlings, including four tropical inbred lines and eight breeding populations that showed complete inhibition of R1-nj. We also demonstrate that the red root marker can be used for haploid identification in germplasm with natural anthocyanin expression in the pericarp. A survey of 546 tropical inbreds and 244 landraces showed that anthocyanin accumulation in the roots of germinating seedlings is very rare compared with anthocyanin accumulation in the seed and leaf sheath tissues. As a result, the red root marker can serve as a highly complementary marker to R1-nj to enable effective identification of haploids within a wide range of tropical maize germplasm.
Tag: greenhouse
Infection potential of farm soils as mycorrhizal inocula for Leucaena leucocephala
A greenhouse experiment was conducted to assess the arbuscular mycorrhizal (AM) fungi inoculum potential for Leucaena leucocephala in a range of nutrient-depleted farm soils in western Kenya. Leucaena was grown in 12 uninoculated farm soils with pH 5.0–6.7, with or without rock P and farmyard manure. Root infection, nodulation, and shoot and root weight were determined 25, 46, and 69 days after planting. Spore concentrations in the farm soils at the start of the experiment ranged from 44 to 126 live spores per 100 g dry soil with 6–10 species per soil, principally Scutellospora spp. and Acaulospora spp. Nodulation was absent or poor in all soils, indicating the need for rhizobial inoculation of species belonging to the leucaena crossinoculation group in this agrosystem. Rock-P alone increased final shoot dry weight by a factor of 1.4, manure alone by 1.8, and rock-P plus manure by 1.9, compared with no ameliorant. Root infection with AM fungi was detected in all soils 25 days after planting and increased linearly in the different farm soils to values of 33–65% 69 days after planting. Soil pH and root infection 25 days after planting accounted for much of the variation in final shoot weight among soils with no amelioront (87%). As early root infection increased from 20 to 40% at soil pH 5.0, the predicted final shoot dry weight was doubled, and the response to ameliorants was reduced by two-thirds. The growth responses to increased infection became smaller as pH increased from 5.0 to 6.5.
Rubber Cultivation Weakened the Soil Methane Sink Function Compared to Natural Forest
The impact of transforming natural forest into rubber plantations on soil function as CH4 sink has not been well understood especially on the seasonal dynamic and changes in underlying soil processes. Aimed to understand how this land use conversion changes the soil CH4 sink we conducted measurements in both natural forests and rubber plantations in Xishuangbanna SW China. Temporal dynamic of soil surface CH4 flux CH4 concentration and isotope signature of 13CH4 in the soil profile at 5 10 30 and 70 cm depth were measured at representative time in dry and rainy season. CH4 uptake by soils in rubber plantations was only 41.8 % of uptake by forest soils with annual CH4 cumulative flux of -2.41±0.28 and -1.01±0.23 kgC ha−1yr−1 for forests and rubber plantations respectively. The CH4 oxidation was stronger in dry season than in rainy season mainly explained by changes in soil moisture. From dry season to rainy season CH4 flux shifted to weak consumption in forest and young rubber plantation or even towards emission in older rubber plantations; CH4 concentration increased in all four depths with higher increment in older rubber plantations. The enrichment of soil CH4 by 13CH4 was higher in forest than in rubber plantations. The decrement of delta 13CH4 from dry to rainy season in both land uses indicated the increased CH4 production in rainy season while the flux showed the net consumption. The CH4 turnover rate suggested that the surface 0–5 cm soil was the most active layer responsible for CH4 oxidation. Conversion the forest into rubber plantation weakened soil CH4 sink function. Seasonal change of CH4 flux and 13CH4 enrichment was larger under rainforest than rubber plantations indicating modified soil water regime under rubber. Converting forest into rubber plantations and rubber cultivation may have profound impact on greenhouse gas emission from soil.