Linear and non-linear regression analysis of genotype X environment interactions in pearl millet

Summary Regression analysis was computed on the grain yield of 15 single cross F₁ hybrids of pearl millet (Pennisetum typhoides (Burm.) S. & H.) evaluated in 20 environments at 19 sites in India to assess the nature of genotype X environment interactions. Linear, quadratic, cubic, twoand three-intersecting straight line models were examined for fit. The interactions of six hybrids viz. MH 110, MH 113, MH 114, MH 115, MH 120 and MBH 110 were explained by the linear regression model. The response of the remaining nine hybrids was largely non-linear. The two and three-intersecting straight line models fit better than the quadratic and cubic models and explained non-linearity of response. The two-intersecting straight line models fit for 6 hybrids MH 106, MH 107, MH 112, MH 116, MH 117 and BJ 104. The response of MH 109 was best explained by a three-intersecting straight line model, but there still existed a significant remainder variation. The truncation of environmental range by assuming moving division points was more efficient than the fixed division points for the segmental regression models. The stability of hybrid varieties on the best fitting model has been discussed.     

A note on the genomic consequences of regular bivalent formation and continued fertility in triploids

The genomic evolution of triploid plants with regular bivalent formation is discussed. The conclusion is reached that although all the progeny of an originally triploid individual will be triploid numerically, only part of the progeny will be triploid genomically. The consequences of this for triploid identification by means of chromosome morphology and isozyme numbers is discussed.     

Measurement and modelling of photosynthetic response of pearl millet to soil phosphorus addition

There have been no studies of the effects of soil P deficiency on pearl millet (Pennisetum glaucum (L.) R. Br.) photosynthesis, despite the fact that P deficiency is the major constraint to pearl millet production in most regions of West Africa. Because current photosynthesis-based crop simulation models do not explicitly take into account P deficiency effects on leaf photosynthesis, they cannot predict millet growth without extensive calibration. We studied the effects of soil addition on leaf P content, photosynthetic rate (A), and whole-plant dry matter production (DM) of non-water-stressed, 28 d pearl millet plants grown in pots containing 6.00 kg of a P-deficient soil. As soil P addition increased from 0 to 155.2 mg P kg^–1 soil, leaf P content increased from 0.65 to 7.0 g kg^–1. Both A and DM had maximal values near 51.7 mg P kg^–1 soil, which corresponded to a leaf P content of 3.2 g kg^–1. Within this range of soil P addition, the slope of A plotted against stomatal conductance (g_s) tripled, and mean leaf internal CO₂ concentration ([CO₂]_i) decreased from 260 to 92 L L^–1, thus indicating that P deficiency limited A through metabolic dysfunction rather than stomatal regulation. Light response curves of A, which changed markedly with P leaf content, were modelled as a single substrate, Michaelis-Menten reaction, using quantum flux as the substrate for each level of soil P addition. An Eadie-Hofstee plot of light response data revealed that both K_M, which is mathematically equivalent to quantum efficiency, and V_max, which is the light-saturated rate of photosynthesis, increased sharply from leaf P contents of 0.6 to 3 g kg^–1, with peak values between 4 and 5 g P kg^–1. Polynomial equations relating K_M and V_max, to leaf P content offered a simple and attractive way of modelling photosynthetic light response for plants of different P status, but this approach is somewhat complicated by the decrease of leaf P content with ontogeny.     

Arachidonic acid-induced hypersensitive cell death as an assay of downy mildew resistance in pearl millet

Arachidonic acid (AA) induces hypersensitive response (HR) on coleoptile/root regions of two-day-old pearl millet seedlings. The response is comparable to the HR induced by the downy mildew pathogen, Sclerospora graminicola. A time gap in the appearance of cell necrosis among genotypes of pearl millet was related to the degree of resistance to downy mildew. Based on the time required for the development of necrotic spots induced by AA, the pearl millet genotypes were categorised as highly resistant/resistant (HR in 3–6 h), susceptible (HR in 7–12 h) and highly susceptible (HR in 13 h and above). The percentage disease incidence in each genotype was compared with the time required for the development of AA-induced HR. The appearance of hypersensitive cell necrosis was rapid in genotypes having high resistance to downy mildew and was slow in genotypes with high susceptibility. This simple method of screening various pearl millet genotypes in the absence of the pathogen aids in identifying the downy mildew resistant/susceptible host cultivars without the risk of introducing the virulent race of the pathogen.     

Correlation and path-coefficient analyses of seed-yield components in pearl millet x elephantgrass hybrids

Correlation and path-coefficient analyses have been successful tools in developing selection criteria. Since increased seed yield is an important goal in our pearl millet x elephantgrass [Pennisetum glaucum (L.) R.Br. x P. purpureum Schum.] hexaploid breeding program, we used correlation and path-coefficient analyses on seed data. This study was conducted to develop appropriate selection criteria by determining the direct and indirect effects of seed-yield components on seed yield plant^-1. Number of tillers plant^-1, panicles tiller^-1, seeds panicle^-1, 100-seed weight, and seed yield plant^-1, were estimated for individual plants in seven families. Phenotypic (r_p) and genetic correlations (r_g) were calculated, and path analyses (phenotypic and genetic) were carried out according to predetermined causal relationships. Phenotypic and genetic correlations differed in several cases due to large environmental variance and covariance. Phenotypically, all components were positively and significantly associated with seed yield plant^-1. Genotypically, only seeds panicle^-1 and 100-seed weight were significantly correlated. These two components were also positively correlated (r _p=0.55, r _g=0.63), so simultaneous improvement for both components would be feasible. Panicles tiller^-1 and seeds panicle^-1 were negatively correlated (r _g=-0.97). In the path analyses, all direct effects of the components on seed yield plant^-1 were positive. Phenotypic indirect effects were not as important as genetic indirect effects. The components seeds panicle^-1 and 100-seed weight influenced seed yield plant^-1 the greatest, both directly and indirectly.Florida Agricultural Experimental Station Journal Series No. R-03339     

Assessment of cytoplasmic differences of near-isonuclear male-sterile lines in pearl millet

Four near-isonuclear polycytoplasmic versions of 81A and two of Pb 402A male-sterile lines of pearl millet (Pennisetum typhoides) were used in factorial matings with five inbred male testers in different combinations in three sets. The cytoplasmic differences were studied for several agronomic traits using mean values and general combining effects (gca) of male-sterile lines, and specific combining ability effects of hybrids. The fertility/ sterility behaviour of different male-sterile lines in crosses with common male parents was also studied. Significant differences among near-isonuclear polycytoplasmic lines were observed in mean values for a few traits such as plant height, leaf length and peduncle length, but the differences for combining ability were more pronounced. The A₃ cytoplasm was a better general combiner than the A₂ cytoplasm for grain yield and both A₂ and A₃ cytoplasms were better general combiners for leaf length and peduncle length. In addition, superiority of A₃ cytoplasm for gca was observed for plant height and ear characters over the A₂ cytoplasm in set II. A differential behaviour of cytoplasms, both in combination with a common pollinator and across pollinators, was observed for several traits. The results provide evidence for the distinctiveness of different cytoplasmic sources in pearl millet and for the influence of cytoplasmic factors on the phenotypic expression of nuclear genes. A diversification of male sterility sources in the breeding of pearl millet hybrids is suggested.     

Influence of A1 cytoplasmic substitution on the downy-mildew incidence of pearl millet

Large-scale cultivation of pearl millet [Pennisetum glaucum (L.) R. Br. F₁ hybrids in India has led to increased incidence of downy-mildew (Sclerospora graminicola). There is concern that the A₁ male-sterile cytoplasm used in all the hybrids released so far is responsible for this increase. The influence of A₁ malesterile cytoplasm on downy-mildew incidence in pearl millet was studied by comparing the disease reaction of 40 pairs of F₁ hybrids, each pair carrying respectively a₁ male-sterile and normal B cytoplasm. Mean downy-mildew incidence was similar in the hybrids carrying either A₁ male-sterile or B cytoplasm. The general combining ability of lines with and without A₁ cytoplasm was found to be similar for downy-mildew incidence. These results indicated that in pearl millet A₁ cytoplasm is not associated with increased downymildew incidence. The possible danger of using only one source of cytoplasm has been briefly discussed.     

Multiple chromosomal interchanges in pearl millet

Summary Intercrossing and irradiation were successfully used in pearl millet (Pennisetum typhoides) to develop multiple interchanges involving up to the total complement of all the chromosomes in one complex. In interchange heterozygotes showing 12 + 1 II and 14, 90.9 and 87.8 per cent of the cells, respectively, had chromosome configurations other than that of 12 and 14 chromosomes. In general, the frequency of such cells resulting from breakdown of the expected complex configuration increased with the increase in the number of translocated chromosomes in the complex. The higher the number of chromosomes involved in the interchange ring, the higher were the pollen and ovule sterility. The results indicated that meiotic instability, deficiency-duplication gametes, and unequal distribution of chromosomes account for increased sterility of multiple interchange heterozygotes. Even though interchanges in pearl millet predominantly show the alternate type of segregation, sterility seems to be the major barrier for the exploitation of the multiple interchange method for gamete selection and the establishment of homozygous lines in this plant species.     

Response of millet and sorghum to a varying water supply around the primary and nodal roots

Background and Aims

Cereals have two root systems. The primary system originates from the embryo when the seed germinates and can support the plant until it produces grain. The nodal system can emerge from stem nodes throughout the plant''s life; its value for yield is unclear and depends on the environment. The aim of this study was to test the role of nodal roots of sorghum and millet in plant growth in response to variation in soil moisture. Sorghum and millet were chosen as both are adapted to dry conditions.

Methods

Sorghum and millet were grown in a split-pot system that allowed the primary and nodal roots to be watered separately.

Key Results

When primary and nodal roots were watered (12 % soil water content; SWC), millet nodal roots were seven times longer than those of sorghum and six times longer than millet plants in dry treatments, mainly from an 8-fold increase in branch root length. When soil was allowed to dry in both compartments, millet nodal roots responded and grew 20 % longer branch roots than in the well-watered control. Sorghum nodal roots were unchanged. When only primary roots received water, nodal roots of both species emerged and elongated into extremely dry soil (0·6–1·5 % SWC), possibly with phloem-delivered water from the primary roots in the moist inner pot. Nodal roots were thick, short, branchless and vertical, indicating a tropism that was more pronounced in millet. Total nodal root length increased in both species when the dry soil was covered with plastic, suggesting that stubble retention or leaf mulching could facilitate nodal roots reaching deeper moist layers in dry climates. Greater nodal root length in millet than in sorghum was associated with increased shoot biomass, water uptake and water use efficiency (shoot mass per water). Millet had a more plastic response than sorghum to moisture around the nodal roots due to (1) faster growth and progression through ontogeny for earlier nodal root branch length and (2) partitioning to nodal root length from primary roots, independent of shoot size.

Conclusions

Nodal and primary roots have distinct responses to soil moisture that depend on species. They can be selected independently in a breeding programme to shape root architecture. A rapid rate of plant development and enhanced responsiveness to local moisture may be traits that favour nodal roots and water use efficiency at no cost to shoot growth.