Effect of cultural methods on Striga (Striga hermonthica (Del.)) Benth management and yield of cereals in the Savanna Zone of Nigeria: a review

Data were obtained from the research done in the Guinea Savanna (Zaria 11°11′N; 070 38′E) and Sudan Savanna (Maiduguri ?11°51′N; 13°15′E) regions of Nigeria, respectively on different cultural methods of Striga control and management. In the Guinea Savanna, trials on the effects of nitrogen on the response of resistant and susceptible upland rice varieties to Striga hermonthica infestation and the effect of resistant and susceptible varieties of maize and crop rotation on Striga infestation was carried out, while the effect of inter-cropping trap crop (Bambaranut) with resistant sorghum varieties on S. hermonthica was studied in the Sudan Savanna Zone of Nigeria. In the Guinea Savanna, it was observed that a combination of upland rice variety, Faro 40 and an application of 90 kg N/ha in the wet season and WAB 56-50 upland rice variety and 120 kg N/ha in the dry season, respectively reduced Striga infestation and produced maximum grain yield. Also, the growing of resistant variety of maize (Across 97ITZ comp. I-W) after 1 or 2 years' rotation with cowpea or soybean was observed not only to be effective in Striga control, but resulted in higher grain yield of maize. In the Sudan Savanna, the use of resistant varieties of sorghum, 1CSV1002 and 1CSV1007 intercropped with bambaranut significantly reduced Striga infestation, but the grain yield of the resistant varieties was low. From these studies, Faro 40 with 90 kg N/ha application rate and WAB56–50 with 120 kg N/ha were suitable for the management of Striga and for higher grain yield of upland rice in both wet and dry seasons, respectively, while Across 97ITZ comp. I-W, resistant maize variety and 1 or 2 years rotation with cowpea or soybean were also the best for the management of S. hermonthica and for higher maize yield in the Guinea Savanna zone. Further research needs to be carried out in the Sudan Savanna to select a high yielding resistant variety of sorghum which when intercropped with bambaranut will not only control Striga infestation but will also give high grain yield.     

Response of sorghum cultivars and striga population to nitrogen fertilization

Summary Findings derived from the present study suggest that Sorghum cultivars differed in their ability to respond to different fertilizer regimes. Not one cultivar consistently showed the same degree of response over all yield components measured. The most responsive cultivars for number of grains/head, straw yield, head weight, and Striga infestation were Karkatib, Dabr 1/1/1/1, Feterita, and T.U.B. 7 resp.Over all yield components measured maximum response to the different fertilizer regimes was realised at 215 kg N/ha. N-fertilization significantly increased host yields and significantly reduced Striga yields. Of all cultivars, Safra was the most efficient in allocating more nutrients to grain production than to straw. No consistent evidence was found to indicate that host responsiveness to nitrogen fertilization would invariably depress Striga infestations. Thus the hypothesis that N-fertilization significantly reduces a Striga attack is untenable as a general statement about all host cultivars.     

Genetic progress in the UNB-2U population of popcorn under recurrent selection in Rio de Janeiro, Brazil

As part of the Universidade Estadual do Norte Fluminense recurrent selection program of popcorn, we evaluated full-sib families of the sixth cycle of recurrent selection and estimated genetic progress for grain yield and expansion capacity. We assessed 200 full-sib families for 10 agronomic traits, in a randomized block design, with two replications within sets in two environments: Campos dos Goytacazes and Itaocara, in the State of Rio de Janeiro, Brazil. There were significant differences for families/"sets" for all traits, indicating genetic variability that could be exploited in future cycles. In the selection of superior progenies, the Mulamba and Mock index gave the best gains for popping expansion (PE) and grain yield (GY), with values of 10.97 and 15.30%, respectively, using random economic weights. By comparing the evolution of the means obtained for PE and GY in the cycles C(0), C(1), C(2), C(3), C(4), C(5), and predicted for C(6), a steady increase was observed for both PE and GY, with the addition of 1.71 mL/g (R(2) = 0.93) and 192.87 kg/ha (R(2) = 0.88), respectively, in each cycle. Given the good performance of this popcorn population in successive cycles of intrapopulation recurrent selection, we expect that a productive variety with high expansion capacity will soon be available for producers in the north and northwest regions of Rio de Janeiro State, Brazil.     

Trends in population parameters and best linear unbiased prediction of progeny performance in a European F2 maize population under modified recurrent full-sib selection

Recurrent selection is a cyclic breeding procedure designed to improve the mean of a population for the trait(s) under selection. Starting from an F₂ population of European flint maize (Zea mays L.) intermated for three generations, we conducted seven cycles of a modified recurrent full-sib (FS) selection scheme. The objectives of our study were to (1) monitor trends across selection cycles in the estimates of the population mean, additive and dominance variances, (2) compare predicted and realized selection responses, and (3) investigate the usefulness of best linear unbiased prediction (BLUP) of progeny performance under the recurrent FS selection scheme applied. Recurrent FS selection was conducted at three locations using a selection rate of 25% for a selection index, based on grain yield and grain moisture. Recombination was performed according to a pseudo-factorial mating scheme, where the selected FS families were divided into an upper-ranking group of parents mated to the lower-ranking group. Variance components were estimated with restricted maximum likelihood. Average grain yield increased 9.1% per cycle, average grain moisture decreased 1.1% per cycle, and the selection index increased 11.2% per cycle. For the three traits we observed, no significant changes in additive and dominance variances occurred, suggesting future selection response at or near current rates of progress. Predictions of FS family performance in Cn+1 based on mean performance of parental FS families in Cn were of equal or higher precision as those based on the mean additive genetic BLUP of their parents, and corresponding correlations were of moderate size only for grain moisture. The significant increase in grain yield combined with the decrease in grain moisture suggest that the F₂ source population with use of a pseudo-factorial mating scheme is an appealing alternative to other types of source materials and random mating schemes commonly used in recurrent selection.     

Genetic changes from introgression of highland Mexican germ plasm into a Corn Belt Dent population of maize

Summary A backcross population (NZS1) of maize (Zea mays L.) was produced by crossing a highland Mexican population with the elite Corn Belt Dent synthetic AS3, and then by backcrossing to AS3. S₁ lines, S₂ lines, and S₂ testcrosses with an elite tester were used to compare the means, correlations, genetic variances, and predicted gains from selection of NZS1 and AS3 for grain yield, grain moisture at harvest, root and stalk lodging in a cool, temperate environment in New Zealand. The S₁ and S₂ lines from NZS1 had lower mean grain yields, higher levels of root lodging and higher mean grain moistures than the S₁ and S₂ lines from AS3. Mean grain yields of testcrosses of NZS1 and AS3 were similar, but NZS1 testcrosses had higher levels of root lodging. Genotypic variances estimated from S₁ and S₂ lines were larger for grain yield and root lodging for NZS1, smaller for grain moisture, and similar for stalk lodging. Predicted gains from selection for grain yield using intrapopulation methods based on the additive-genetic variance were larger for NZS1, but predicted gains for testcross selection were similar for the two populations. Lines with high combining ability for grain yield and acceptable grain moisture in combination with the tester occurred in NZS1. Because of the higher additive-genetic variance and the occurrence of lines with high combining ability for grain yield, we concluded that populations including highland Mexican germ plasm should be valuable for recurrent selection programs in New Zealand and in other cool, temperate regions.     

Doubled haploid versus S1 family recurrent selection for testcross performance in a maize population

Theoretically, in a recurrent selection program, the use of doubled haploids (DH) can increase genetic advance per unit of time. To evaluate the efficiency expected from the use of DH for the improvement of grain yield in a maize (Zea mays L.) population, two recurrent selection programs for testcross performance were initiated using testcross progenies from DH lines and S₁ families. In 4 years one selection cycle using DH and two selection cycles using S₁ families were carried out with the same selection intensity for both methods. As expected, testcross genetic variance was twice as high among DH lines as among S₁ families. The predicted genetic gain was 8.2% for the DH selection cycle, and 10.6% for the two S₁ selection cycles, giving a per year advantage of 29% for the S₁ family method over the DH method with a cycle of 4 years. With a 3-year cycle for the DH method, both methods were expected to be equivalent. Using a tester related to the one used for selection, the genetic gains obtained were equivalent for both methods: 6.6% for the DH cycle and 7.0% for the two S₁ cycles. With a 3-year cycle for the DH method, the advantage would have been in favor of DH method. Furthermore, the DH method has the advantage of simultaneously producing lines that are directly usable as parents of a hybrid. Thus, if the genetic advance per unit of time is evaluated at the level of developed varieties even with the same or with a lower genetic advance in population improvement, the DH method appears to be the most efficient.     

Morpho-physiology and maize grain yield under periodic soil flooding in successive selection cycles

This study was carried out to evaluate maize plants of different recurrent selection cycles of the variety (Zea mays L.—Saracura-BRS-4154) regarded to genetic gains, morphophysiology, and grain yield, achieved over the selection cycles under intermittent flooding of the soil. This variety has the capacity to survive and produce in temporarily flooded soils and was developed by the National Maize and Sorghum Research Center (EMBRAPA). The experiment was conducted in greenhouse by using ten alternating selection cycles (Cycle 1–18) and BR 107 a variety known for its susceptibility to flooding. The flooding initiated at six-leaf stage by applying 50 mm of water three times a week. At flowering, the following parameters were evaluated: rate of leaf photosynthesis, stomatal conductance, intercellular CO₂ concentration, transpiration rate, photosynthetically active leaf area, root porosity, relative chlorophyll content, grain yield, harvest index, ear length, and interval between male and female flowering. Yield as a function of root porosity and photosynthesis were also evaluated. An index was created in this study, in order to help the discussion of the characteristics evaluated, it was called “Relative Tolerance Value—RTV”, only gaseous exchange measurements was not included in this index. By the way, it was observed throughout the selection cycles an increase in all gaseous exchange parameters, being the cycle 18, the one which presented the greatest averages. RTV for leaf area showed the greatest values for cycles 7 and 18, whereas root porosity, chlorophyll relative content, and harvest index, the greater RTV values were found in cycles 17 and 18. The largest grain yield RTV was observed in cycle 7, followed by cycles 13, 15, and 18. Flooding resulted in longer Anthesis-Silking Interval, especially for the first cycles. At flooding condition, grain yield was strongly related to root porosity (R ² = 0.66). These results showed that the selection cycles of “Saracura” maize improved some morphophysiologic characters, which favor their survival in flooded environments, also resulting in higher productivity.     

Variability in host plant resistance of Sorghum to Striga Hermonthica infestation in West Africa

Fourteen elite sorghum lines were evaluated for their resistance to Striga hermonthica at three locations in Nigeria and Mali. Results showed that many of the lines especially MALISOR 84-1, SAMSORG 41, 97-SB-F5DT-64 (Keninkédié) and the check SRN 39 remained resistant to Striga in all locations with low emerged Striga counts, while SAMSORG 14 had the highest Striga infestation in all locations. Considerable variation in reaction to Striga infestation was observed on Séguètana, 97-SB-F5DT-63 (Wasa), 97-SB-F5DT-65, CMDT 38, CMDT 39 and CMDT 45 which were susceptible to Striga at Samaru, Nigeria but were resistant to Striga at both locations in Mali. Based on low Striga resistance and high grain yield, lines MALISOR 84-1, SAMSORG 41, 97-SB-F5DT-64, 97-SB-F5DT-65, CMDT 39 and SAMSORT 14 have been nominated for wider evaluation across more West African countries.     

Genomic regions involved in response to grain yield selection at high and low nitrogen fertilization in maize

In order to validate the role of genomic regions involved in nitrogen use efficiency and detected in a population of recombinant inbred lines (RIL), we have applied from the same population a recurrent selection for adaptation to low N-input (N0) and to high N-input (N1). Variation of allele frequency at neutral marker during the two cycles of recurrent selection may provide information about markers linked to QTLs. Significant temporal variation of allele frequency was investigated using the test of Waples, which tests the hypothesis of genetic drift versus selection. Most genomic regions (12/19) responding to selection were detected for selection at high N-input and only two were common to selection at high and low N-inputs. This was consistent with the greater grain yield response to selection observed for the population selected under high N-input compared with the population selected under low N-input, when they were evaluated at high N-fertilization. In contrast, when they were evaluated at low N-input both types of selection gave similar yield. As was expected, in the first cycle we observed selection of markers linked to grain yield QTLs. In the course of the second cycle three situations were observed: the confirmation of most regions already selected in C1 including all C1 regions overlapping with grain yield QTLs; the non-confirmation of some C1 regions (2/9); and the identification of new genomic zones (10/17). The detected marker–QTL associations revealed the consistency of the involvement of some traits, such as root architecture and glutamine synthetase activity, which would be of major importance for grain yield setting whatever the nitrogen fertilization.     

Chemical weed management in wheat at higher altitudes

To evaluate the effect of different herbicides for controlling weeds in wheat (variety Fakhr-i-Sarhad),at higher attitude, an experiment was conducted at Agriculture Research Station, Chitral during Rabi season 2003-04, using Randomized Complete Block Design, keeping four replications. The experiment, sown in November comprised of eight treatments, viz; seven herbicides and a weedy check. Each treatment consisted of 5 rows each 30 cm apart and 5 m long thus giving a total size of 5 m x 1.5 m. The herbicides used included; terbutryn + triasulfuron at 0.16 kg, 2,4-D at 0.7 kg, fenoxaprop-P-ethyl at 0.93 kg, clodinafop at 0.05 kg, bromoxynil + MCPA at 0.49 kg, carfentrazon-ethyl at 0.02 kg and isoproturon at 1.0 kg a.i ha(-1). The data were recorded on weed kill efficiency (%), fresh weed biomass (kg ha(-1)), plant height (cm), spike length (cm), number of tillers m(-2), number of grains spike(-1), thousand grains weight (g), biological yield (kg ha(-1)), grain yield (kg ha(-1)) and harvest index (%). The data recorded on weed kill efficiency, weed biomass (kg ha1), grains yield (kg ha(-1)) and harvest index (%) were significantly affected by the different herbicidal treatments. Statistically isoproturon treatment exhibited the best performance, with maximum weed kill efficiency (48.26%) and minimum fresh weed biomass (433.3 kg ha(-1)) as compared to weedy check (6 %) and (1102 kg ha(-1)), respectively. Similarly, the spike length (8.34 cm), number of tillers (427 m(-2)), number of grains spike(-1) (38.0), thousand grains weight (39.85 g), biological yield (8475 kg ha(-1)), grain yield (2530 kg ha(-1)) and harvest index (31.3%) were the highest in isoproturon treatments as compared to weedy check having (7.64 cm), (356 m(-2)), (34.1), (37.12 g), (6858 kg), (1913 kg ha(-1)) and (27%), respectively.     

Role of thiourea in improving productivity of wheat (Triticum aestivum L.)

The role of thiourea (TU), a sulfhydryl compound, was assessed in wheat via soil and foliar treatments. Results showed that at 30 days after flowering, soil-applied TU treatments did not influence dry matter accumulation or its distribution in leaves, stems, and ears, but foliar-applied treatments brought about significant effects varying with the timing of spray. At harvest, however, soil-applied treatment of 10 kg/ha TU increased the number of ears, grains/ear, weight/grain, biological yield (total above ground biomass), grain yield, and harvest index. Grain yield increased by 17.3% over control. Soil-applied 20 kg/ha TU increased the grain yield by 1.6% over control. Foliar applied treatment of 0.5 kg/ha TU at tillering increased the number of ears, grains/ear, weight/grain, biological yield, grain yield, and harvest index. Grain yield increased by 15.2% over control. Foliar spray of 0.5 kg/ha TU at flowering tended to improve only weight/grain, but biological yield and grain yield increased significantly. Grain yield increased by 6.6% over control. TU spray at both tillering and flowering increased the number of ears, grains/ear, weight/grain, biological yield, grain yield, and harvest index. Grain yield increased by 23.9% over control, and when compared with spray at tillering there was a significant increase of 7.5%. Thus, two foliar sprays of thiourea, at tillering and at flowering, at 1 kg/ha can be recommended for improving wheat productivity.Abbreviations TU thiourea - DMA dry matter accumulation - DMD dry matter distribution     

Genetic drift and selection effects of modified recurrent full-sib selection programs in two F2 populations of European flint maize

Selection response of a modified recurrent full-sib (FS) selection scheme conducted in two European flint F₂ maize (Zea mays L.) populations was re-evaluated. Our objectives were to (1) determine the selection response for per se and testcross performance in both populations and (2) separate genetic effects due to selection from those due to random genetic drift. Modified recurrent FS selection was conducted at three locations using an effective population size N _e = 32 and a selection rate of 25% for a selection index, based on grain yield and grain moisture. Recombination was performed according to a pseudo-factorial mating scheme. Selection response was assessed using a population diallel including the source population and advanced selection cycles, as well as testcrosses with unrelatesd inbred line testers and the parental F₁ generation. Selection response per cycle was significant for grain yield and grain moisture in both populations. Effects of random genetic drift caused only a small reduction in the selection response. No significant selection response was observed for testcrosses, suggesting that for heterotic traits, such as grain yield, a high frequency of favorable alleles in the elite tester masked the effects of genes segregating in the populations. We conclude that our modified recurrent FS selection is an alternative to other commonly applied intrapopulation recurrent selection schemes, and some of its features may also be useful for increasing the efficiency of interpopulation recurrent selection programs.     

Effects of selection for resistance to Sesamia nonagrioides on maize yield,performance and stability under infestation with Sesamia nonagrioides and Ostrinia nubilalis in Spain

A maize synthetic population was improved for resistance to the Mediterranean corn borer (MCB, Sesamia nonagrioides) while maintaining yield. The objectives of this research were to investigate whether yield and yield stability of the maize synthetic population named EPS12 were affected by selection for MCB resistance; also to determine which genotypic and environmental covariates could explain the genotype (G), environment (E) and genotype × environment (GE) effects for yield under corn borer infestation. Plants from three cycles of selection and their testcrosses to three inbred testers (A639, B93 and EP42) were evaluated at two locations in 2 years, under MCB and European corn borer infestations. After selection EPS12 was a more stable genotype. Hybrids derived from crosses between B93 and inbreds obtained from the initial cycles of selection could be recommended for cultivation in northern Spain. The yield of crosses between cycles of selection and testers increased when there were fewer days with temperatures >25°C and higher mean maximum temperatures. Differences in yield among these genotypes were mostly explained by resistance to corn borer attack. In general, among EPS12-derived materials, genetic characteristics that contribute to increased grain yield were also responsible for increased abiotic stress tolerance.     

Evaluation and retrospective optimization of genomic selection for yield and disease resistance in spring barley

The general applicability of genomic selection (GS) to plant breeding and principles guiding its use have been established by simulation and empirical cross-validation studies. More recently, studies have demonstrated genetic gains over multiple cycles of selection in a variety of crop species. In this study, we provide additional evidence for the effectiveness of GS in an actual breeding program by demonstrating significant gains of 186.1 kg ha^?1 and ??1.85 ppm for grain yield and deoxynivalenol, respectively, two unfavorably correlated quantitative traits, across 3 cycles of selection in a spring six-row barley breeding population. With its general effectiveness established, the next step is to increase the accuracy of predictions used in GS and thereby increase genetic gains. For this, we first showed that updating the training population (TP) with phenotyped lines from recent breeding cycles, specifically selected lines, had an overall positive effect on prediction accuracy. Additionally, we investigated four recently proposed algorithms that seek to optimize the composition of a TP. Overall, the optimization algorithms improved prediction accuracy when compared to a randomly selected TP subset of the same size, but which algorithm performed best was dependent on the trait being predicted and other factors discussed within. This retrospective investigation highlights the importance of maintaining and optimizing the TP when using GS in applied breeding to maximize prediction accuracy, thereby maximizing gain from selection and resource utilization efficiency.     

Estimates of genetic variance in an F2 maize population

Maize (Zea mays L.) breeders have used several genetic-statistical models to study the inheritance of quantitative traits. These models provide information on the importance of additive, dominance, and epistatic genetic variance for a quantitative trait. Estimates of genetic variances are useful in understanding heterosis and determining the response to selection. The objectives of this study were to estimate additive and dominance genetic variances and the average level of dominance for an F2 population derived from the B73 x Mo17 hybrid and use weighted least squares to determine the importance of digenic epistatic variances relative to additive and dominance variances. Genetic variances were estimated using Design III and weighted least squares analyses. Both analyses determined that dominance variance was more important than additive variance for grain yield. For other traits, additive genetic variance was more important than dominance variance. The average level of dominance suggests either overdominant gene effects were present for grain yield or pseudo-overdominance because of linkage disequilibrium in the F2 population. Epistatic variances generally were not significantly different from zero and therefore were relatively less important than additive and dominance variances. For several traits estimates of additive by additive epistatic variance decreased estimates of additive genetic variance, but generally the decrease in additive genetic variance was not significant.     

Identification of QTLs associated with physiological nitrogen use efficiency in rice

Demand for low-input sustainable crop cultivation is increasing to meet the need for environment-friendly agriculture. Consequently, developing genotypes with high nutrient use efficiency is one of the major objectives of crop breeding programs. This study was conducted to identify QTLs for traits associated with physiological nitrogen use efficiency (PNUE). A recombinant inbred population (DT-RILs) between Dasanbyeo (a tongil type rice, derived from an indica x japonica cross and similar to indica in its genetic make-up) and TR22183 (a Chinese japonica variety) consisting of 166 F8 lines was developed and used for mapping. A frame map of 1,409 cM containing 113 SSR and 103 STS markers with an average interval of 6.5 cM between adjacent marker loci was constructed using the DT-RILs. The RILs were cultivated in ordinary-N (N-P2O5-K2O = 100-80-80 kg/ha) and low-N (N-P2O5-K2O= 50-80-80 kg/ha) (100 kg/ha) conditions. PNUE was positively correlated with the harvest index and grain yield in both conditions. Twenty single QTLs (S-QTLs) and 58 pairs of epistatic loci (E-QTLs) were identified for the nitrogen concentration of grain, nitrogen concentration of straw, nitrogen content of shoot, harvest index, grain yield, straw yield and PNUE in both conditions. The phenotypic variance explained by these S-QTLs and E-QTLs ranged from 11.1 to 44.3% and from 16.0% to 63.6% , respectively. The total phenotypic variance explained by all the QTLs for each trait ranged from 35.8% to 71.3%, showing that the expression of PNUE and related characters depends significantly upon genetic factors. Both S-QTLs and E-QTLs may be useful for marker-assisted selection (MAS) to develop higher PNUE genotypes.     

Short-term effects of rabbit grazing on a degraded short- tussock grassland in Central Otago

Rabbits are serious economic and environmental pests in New Zealand's semi arid lands, yet there is surprisingly little quantitative information about their grazing impacts. This paper describes the shortterm gains in pasture yield following protection from rabbit grazing in a rabbit-prone, dry tussock grassland community in Central Otago. During the four most productive plant growing months of 1994 (September to December), a six-fold increase in pasture yield was observed after protection from rabbit grazing (139 kg dry weight ha(-1) with rabbits cf. 853 kg DW ha(-1) without rabbits). Rabbit counts were 30 to 42 rabbits per spotlight km. The following four months (January to April) were characterised by reduced pasture growth (3 kg DW/ha with rabbits cf. 337 kg DW ha(-1) without rabbits) and higher rabbit numbers (42-76 rabbits per spotlight km), and was a critical period of herbage depletion. These substantial differences in pasture yield indicate the potential benefits for pastoral production and land conservation following protection from rabbits.     

Effects of nitrogen and potassium combinations on yields and infestations of maize by Busseola fusca (Lepidoptera: Noctuidae) in the humid forest of Cameroon

Field trials were set up in the humid forest zone of Cameroon to investigate the effects of combinations of different rates of nitrogen (N) (0, 60, and 120 kg N ha(-1)) and potassium (K) (0, 80, and 160 kg K ha(-1)) applied to the soil on the incidence and damage of the noctuid stemborer Busseola fusca (Fuller), and on maize, Zea mays L., yield. Each N/K combination had an insecticide control to assess yield losses due to borers. In contrast to N, K had no effect on plant growth and borer incidence and damage. Across seasons and days after planting, total plant dry matter (DM) production increased with N level and it was 1.2-1.9 and 1.7-2.2 times, respectively, higher at 60 and 120 kg N ha(-1) compared with 0 kg N ha(-1). Total DM at harvest was strongly related to the N content of the plant at 63 d after planting. At the early growth stage, borer abundance and stem tunneling tended to increase with N level, but percentages of dead hearts did not vary with treatment. Maize grain yields increased linearly with N level, but grain yield losses decreased depending on season. Grain yield losses were 11-18.2 times higher with 0 kg N ha(-1) compared with 120 kg N ha(-1). The findings so far indicated that, soil application of N improves the nutritional status of maize, which consequently enhanced its tolerance to stemborer attacks. Improving soil fertility can thus be a very effective means of complementing integrated stemborer control in the humid forest zone of Cameroon.     

Analysis of Covariation of Grain Yield and Dry Matter Yield for Breeding Dual Use Hybrid Rye

Winter rye (Secale cereale L.) is becoming increasingly important as substrate for biogas production in Central Europe. Dry matter yield has evolved as a breeding goal comparably important to the traditional grain yield. We analyzed the covariation between both traits and tested other agronomic traits for their correlation to dry matter yield that could be used for prediction of biomass yield. A set of 258 experimental hybrids were tested for dry matter yield harvested at late milk stage and grain yield harvested at full ripening at three to four locations in Germany in 2011 and 2012. We observed a wide range of dry matter yield (10–24 Mg ha^?1) and grain yield (6–15 Mg ha^?1) among testcross progenies. Genetic variances were significantly (P?<?0.01) different from zero for all traits. High entry-mean heritabilities (0.92–0.94) were found for plant height measurements and moderate heritabilities for grain and dry matter yield (0.52 and 0.49, respectively). Relative efficiencies for selection of dry matter yield estimated by second (EC 51–55) and third (EC 73) measurements of plant height were 1.24 and 0.98 respectively, compared to 0.52 for grain yield. Indirect selection for high dry matter yield using late plant height measurements should be successful. Using grain yield for indirect selection was less effective. The observed broad genetic variation for biomass yield in elite hybrid rye gives good prospects for the use as a resource of renewable energy. Plant height is a good predictor of dry matter yield but should be selected together with improved lodging resistance.     

Spatial distribution and population dynamics of Striga hermonthica seeds in naturally infested farm soils

Densities and spatial distribution in soil of seeds of Striga hermonthica were analysed for four naturally infested farm fields in Western Kenya. A revised method for extraction of Striga seeds from soil was used, combining centrifugation with existing techniques based on flotation. Tests showed that 85% of Striga seeds were retrieved from soil samples. In all fields the majority of seeds were found in the plough layer (0 – 20 cm). New seeds entering the soil from the surface after seed shedding created a strong gradient with depth. Downward penetration from the soil surface was larger in sandy soil than in clay soil. In tilled soils no significant vertical density gradient was found within the plough layer. At a fine scale (0.2 m) seed densities showed little horizontal variation, but significant differences in seed densities in the horizontal plane were found at larger scale distances (several m) between locations in all fields. At 125 days after sowing the estimated average number of seeds produced per emerged Striga shoot was 4,827, excluding an approximately similar amount of seeds present in maturing capsules. The estimated average number of seeds produced per mature Striga seed capsule was 1188. Large seasonal fluctuations in the Striga seedbank were measured. An average net increase of 88,825 Striga seeds m^-2 (equivalent to 340%) was calculated from seedbank analyses in 16 sorghum plots. The level of Striga infestation in one field had decreased by 62% from 34,250 seeds m^-2 to 13,125 seeds m^-2 after keeping it fallow for a year. A sharp decline in Striga seed density was found in samples taken at increasing distances from highly infested fields, irrespective of wind direction or slope, suggesting very limited dispersal of Striga seeds by wind or water. Parasite emergence was non-linearly related to initial Striga seed densities in the soil, but this relationship was only observable at the scale of individual plant holes. Seed production was also non-linearly related to numbers of emerged parasites, when measured at plot scale (25 m²), but not at the scale of individual plant holes. In the fields we studied, seed densities below levels of 13,000 Striga seeds m^-2 could be considered to suppress the number of emerging parasites. However, if two or three emerged Striga plants per m^-2 were left to seed, enough seeds would be produced to keep the seedbank in balance.