Screening Maize for Tolerance to Striga hermonthica

Striga hermonthica is a widespread parasitic weed in Africa, causing severe damages to the major cereal crops: millet, sorghum and maize. Considering the subsistence nature of farming in Africa, the development of resistant or tolerant varieties is the most promising cost-effective approach to overcoming the weed problem. A simple, inexpensive and sufficiently uniform infestation technique has been developed by the research department of AgSeeds Ltd., Zaria, Nigeria, which is based on mulching a field with mature Striga plants collected in neighbouring farmers' sorghum fields. With this method, rapid progress was achieved in the development of experimental maize hybrids with high levels of tolerance to S. Hermonthica and good yield potential. Among 34 lines with improved tolerance, two (nos. 74 and 785) showed particularly high levels of tolerance. The hybrid between these two lines had a significantly higher yield (47.6 %) under Striga infestation than the tolerant check 8322-13 developed by IITA.     

Development of synthetic maize populations for resistance to Striga hermonthica

The parasitic witchweed, Striga hermonthica (Del.) Benth, is the greatest biological constraint for cereal crop production by resource-poor farmers in sub-Saharan Africa. Maize, Zea mays L., is a widely grown cereal crop in this region (22 × 10⁶ ha). Striga-resistant maize populations were produced and tested as half-sib families in West and Central Africa. Three populations with white (W), yellow (Y), or mixed (Y/W) grain colour were formed by: (1) intercrossing Striga resistant maize inbred lines followed by two generations of random mating; (2) testing far under artificially induced S. hermonthica infestations in Nigeria, Cameroon, and Ivory Coast and selection of resistant families; (3) two generations of random mating; and (4) two years of testing for resistance. Striga-resistant synthetic W, Y and Y/W populations were produced by compositing resistant half-sib families. Outstanding performance in grain yields and host plant resistance was observed. Maize damage ratings and number of harvested ears were highly correlated with grain yield. High variation was observed for Striga emergence counts. The populations have combined resistance to Striga, maize streak virus (MSV), and other major biotic constraints for maize cultivation in Africa, thus providing the opportunity for improved sustainable maize production under stress environments. Breeder's seed of these synthetic varieties are being multiplied for distribution to national programmes.     

CO<Subscript>2</Subscript>-assimilation and chlorophyll fluorescence as indirect selection criteria for host tolerance against <Emphasis Type="Italic">Striga</Emphasis>

Striga hermonthica (Del.) Benth. is a parasitic weed on tropical cereals causing serious yield losses in Africa. The use of host crop varieties with improved resistance and tolerance against this parasite is a key component of an integrated control strategy. Breeding for tolerance is however seriously hampered by the absence of reliable and yet practical selection measures. The observation that the photosynthetic rate of tolerant genotypes is less sensitive to Striga infection was used as a starting point to search for suitable selection measures. In a greenhouse pot experiment the effect of Striga infection on the photosynthesis of four sorghum (Sorghum bicolor [L.] Moench) genotypes, differing in Striga tolerance level, was measured at three moments in time (26, 48 and 75 days after sowing). Genotypes were CK60-B, E36-1, Framida and Tiémarifing. Measurements involved CO₂-assimilation (A) and three chlorophyll fluorescence characteristics (electron transport rate through photosystem II [ETR], photochemical [Pq] and non-photochemical quenching [NPq]). Striga infection negatively affected A, ETR and Pq. Based on A and Pq, genotypes with superior levels of tolerance (Tiémarifing) could be discriminated from genotypes with superior level of resistance (Framida). Both A and Pq showed high heritabilities and consequently clear and predictable differences between genotypes. Using discriminative ability, heritability and cost effectiveness as main criteria, photochemical quenching (Pq) was concluded to possess the highest potential to serve as indirect selection measure for host plant tolerance to Striga. Screening should preferably be conducted at relatively high Striga infestation levels, between Striga emergence and host plant flowering.     

Expression of mature plant resistance to Striga hermonthica in maize

Twelve maize genotypes with different degrees of resistance were evaluated in plots inoculated with seeds of the phytoparasite Striga hermonthica (Del.) Benth. and in Striga-free (control) plots for three seasons between 1991 and 1993. Resistant genotypes, although showing similar levels of underground infection as susceptible 9 weeks after maize planting (WAP), had significantly fewer emerged parasitic plants and sustained lower damage. Host damage was not determined by the severity of infection. Percent height and dry matter reductions increased from 3 to 6 WAP for resistant and susceptible genotypes. While percent height and dry matter reductions for resistant genotypes declined at 9 and 12 WAP, susceptible genotypes either maintained or increased their levels of damage. Correlation between the severity of height and dry matter reductions at the vegetative (3 and 6 WAP) and reproductive (9 and 12 WAP) stages of maize growth were not significant, indicating that damage at early stages of growth cannot be used to predict mature plant response. Maize damage score (1–9) at 8 WAP, a non destructive and composite shoot indicator of host performance under Striga infestation, was significantly correlated (r = 0.88, r = 0.82; p < 0.01) to the level of shoot reduction at mature plant stages. Emerged Striga count at 8 WAP was significantly correlated (r = 0.98, p < 0.01) to the count at 10 WAP, the time when parasite emergence was highest. Under high and uniform infestation, mature plant resistance can be detected at 8 WAP, the onset of flowering in maize. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inheritance of Resistance to Striga in Sorghum Genotype SRN39

Striga hermonthica (Del.) Benth., a parasitic weed of grasses, causes major yield reductions in the principal cereal crops of semi-arid Africa. Cultivar resistance is the most economic control measure, since adapted, resistant cultivars can be grown without additional input from the subsistence farmer. Information on the genetics of resistance to S. hermonthica is scant. This is partially attributable to the rarity of germplasms which exhibit stable resistance across geographical regions. The objective of this study was to determine if the stable resistance observed in sorghum [Sorghum bicolor (L.) Moench] cultivar SRN39 is heritable. Crosses were made between SRN39 and a susceptible parent, P954063. Parental, F₁, F₂ and backcross generations were grown in infested pots and development of both host and parasite was monitored. Significant variation among genotypes was observed for both host traits and effects on parasite populations. The F₁ did not differ significantly in Striga resistance from the susceptible parent, suggesting recessive inheritance. However, hybrid vigor was exhibited by the F₁ which yielded and developed as well as the resistant parent. Broad sense heritability ranged from 0.23 to 0.55 for host traits and from 0.10 to 0.43 for effect of genotypes on the Striga population. Joint scaling tests showed that observed variation in each host or parasite trait consisted of additive and dominance components, suggesting possible progress could be made with appropriate selection schemes.     

Mechanisms of resistance to shoot fly, <Emphasis Type="Italic">Atherigona soccata</Emphasis> in sorghum

Summary Sorghum shoot fly, Atherigona soccata (Rondani) is an important pest of sorghum in Asia, Africa, and Mediterranean Europe, and host plant resistance is an important component for the management of this pest. The levels of resistance in the cultivated germplasm are low to moderate, and therefore, it is important to identify genotypes with different mechanisms of resistance to pyramid the resistance genes. We studied the antixenosis for oviposition, antibiosis, and tolerance components of resistance in a diverse array of shoot fly-resistant and -susceptible genotypes. The main plants and tillers of SFCR 151, ICSV 705, SFCR 125, and, IS 18551 experienced lower shoot fly deadhearts at 28 days after seedling emergence, produced more number of productive tillers. The insects fed on these genotypes also exhibited longer larval period (10.1–11.0 days compared to 9.3 days on Swarna), lower larval survival and adult emergence (54.7–67.8 and 46.7–52.2% compared to 73.3 and 60.6% on Swarna, respectively), and lower growth and adult emergence indices as compared to the susceptible check, Swarna. Physico-chemical traits such as leaf glossiness, trichome density, and plumule and leaf sheath pigmentation were found to be associated with resistance, and chlorophyll content, leaf surface wetness, seedling vigor, and waxy bloom with susceptibility to shoot fly and explained 88.5% of the total variation in deadhearts. Step-wise regression indicated that 90.4% of the total variation in deadhearts was due to leaf glossiness and trichome density. The direct and indirect effects, correlation coefficients, multiple and step-wise regression analysis suggested that deadhearts, plants with eggs, leaf glossiness, trichomes on the abaxial surface of the leaf, and leaf sheath pigmentation can be used as marker traits to select for resistance to shoot fly, A. soccata in sorghum.     

Effect of cytoplasmic male-sterility in sorghum on host plant interaction with sorghum midge,Contarinia sorghicola

Summary Sorghum midge, Contarinia sorghicola Coq. (Diptera: Cecidomyiidae) is one of the most important pests of grain sorghum worldwide. We studied the reaction of midge-resistant and midge-susceptible genic-cytoplasmic male-sterile (A-lines) and their maintainers (B-lines), and the effect of resistant and susceptible restorers on sorghum midge. Midge damage and adult emergence were significantly lower on the B-lines of midge-resistant genotypes (PM 7061 and PM 7068) than their corresponding A-lines, while the reverse was true for the midge-susceptible genotypes (296A and ICSA 42). Differences in midge damage and the number of midges emerged were not significant between the midge-resistant and midge-susceptible A-lines when infested without pollination (except midge emergence on PM 7061A). Pollination with a midge-resistant restorer (DJ6541) reduced midge emergence significantly in one of two seasons. Source of pollen did not influence midge emergence on the highly-resistant A-line, PM 7061A. The implications of these observations in the development of midge-resistant hybrids were discussed.     

Characterization and genetic control of germination-emergence responses of grain sorghum to salinity

Summary When grain sorghum is grown in saline soils, one cause of low yield is poor crop establishment. The objectives of this study were to assess the response of grain sorghum to salinity in the germination-emergence stages, study the inheritance of salt tolerance at this stage, and determine the relative contribution to final emergence of salt effects during imbibition, and after onset of germination. Twelve inbred lines and 18 F1 hybrids, resulting from an incomplete 6×6 factorial mating design, were tested for germination and emergence in folded paper at 10 salt concentrations, from 1.8 to 36 dSm^-1. The mean EC₅₀ (the electrical conductivity at which the variable score declines by 50%) for emerged seedlings production was 21.2 dSm^-1. Large genotypic differences were observed for salt tolerance at germination and emergence stages, which were not related to the viability of seeds, and poorly related to seed weight (considered as an estimate of intrinsic seed vigor). In the hybrids, these differences were due to SCA and female GCA for emergence, and female GCA for germination, though the male GCA was also significant for both characters. Line per se performance was significantly correlated to individual GCA estimates for emergence, but not for germination. Heterosis was only detected in three crosses for final emergence and in one cross for germination. The genetic differences in final emergence were mainly due to effects occurring after the onset of germination rather than a consequence of effects during imbibition.     

Resistance of cowpea and cereals to the parasitic angiospermStriga

Summary Striga species are parasitic angiosperms that attack many crops grown by subsistence farmers in sub-Saharan Africa and India. Control of the parasite is difficult and genetically resistant crops are the most feasible and appropriate solution. In cowpea, complete resistance toStriga gesnerioides has been identified. Breeding for resistance in sorghum has identified varieties with good resistance toS. asiatica in Africa and India. One variety was also resistant toS. hermonthica in W. Africa. No such resistance toStriga has been found in maize or millets.Resistant varieties have usually been sought by screening germplasm in fields naturally infested withStriga. However, laboratory techniques have also been developed, including anin vitro growth system used to screen cowpeas for resistance toS. gesnerioides. Two new sources of resistance in cowpea have been identified using the system. The technique has also been used to investigate the mechanisms of resistance in this crop. Two mechanisms have been characterised, both were expressed after penetration of cowpea roots by the parasite.The resistance of some sorghum varieties toStriga is controlled by recessive genes. In cowpea, resistance toStriga is controlled by single dominant genes. The genes for resistance are currently being transferred to cowpea varieties which are high yielding or adapted to local agronomic conditions. OneStriga resistant cowpea variety, Suvita-2, is already being grown widely by farmers in Mali. Reports of breakdown of resistance in cowpea toStriga have not yet been confirmed, but a wider genetic base to the resistance is essential to ensure durability ofStriga resistance.Abbreviations ICRISAT International Crops Research Institute for the Semi-Arid Tropics - IITA International Institute of Tropical Agriculture - LARS Long Ashton Research Station - SAFGRAD Semi-Arid Food Grain Research and Development     

Cytoplasmic male-sterility and source of pollen influence the expression of resistance to sorghum midge, Stenodiplosis sorghicola

Sorghum midge, Stenodiplosis (Contarinia) sorghicola (Coquillett), is an important pest of grain sorghum, and host plant resistance is an important aspect of control of this pest. This research investigated how cytoplasmic male-sterility and source of pollen influence the expression of resistance to sorghum midge. Sorghum midge emergence was significantly lower in panicles of midge-resistant and midge-susceptible cytoplasmic male-sterile lines when pollinated with AF 28 - a midge-resistant restorer line, than those pollinated with Swarna - a midge susceptible restorer line, indicating the presence of xenia effects. Maintainer lines (B-lines) of midge-resistant parents had significantly lower numbers of eggs and larvae than the B-lines of midge-susceptible parents. Male-sterile lines of the both midge-resistant and midge-susceptible lines were equally susceptible, indicating that resistance to sorghum midge is influenced by factors in the cytoplasm of the B-line. These findings will have an important bearing on the production of hybrids with resistance to insects. This revised version was published online in August 2006 with corrections to the Cover Date.     

Heritability estimates of variation for NaCl tolerance in Sorghum bicolor (L.) Moench seedlings

Summary Data on root lengths of two-week-old seedlings of 51 Sorghum bicolor (L.) Moench accessions germinated in 50, 100, 150, 175, and 200 mM NaCl solutions were used to estimate broad sense heritabilities of variation for salinity tolerance.Estimates of broad sense heritabilities ranged from 0.38 to 0.73, the highest being in 50 mM NaCl, suggesting that there is potential for improving salinity tolerance in the species through selection and breeding.     

Evaluation of greenhouse inoculation techniques to screen sorghum for resistance to downy mildew

Summary Six inoculation techniques were compared for the artificial promotion of downy mildew (Peronosclerospora sorghi) in sorghum. These were (1) sprouted seeds incubated between sporulating infected leaves, (2) sprouted seeds depped in conidial suspension, (3) sprouted seeds sprayed with conidial suspension, (4) seedlings at plumule stage inoculated with drops of a conidial suspension, (5) seedlings at plumule stage sprayed with a conidial suspension, and (6) seedling showered with conidia falling from infected leaves. Seedlings at the one-leaf stage sprayed with a conidial suspension (6 × 10⁵ ml^-1) showed the highest systemic infection (100%) in the susceptible lines IS 643 and IS 18433. This technique is effective, repeatable, and allows the deposition of a conidial suspension as a fine mist on the entire seedling surface. In the greenhouse, the technique was used to test the downy mildew reaction of genotypes previously reported as resistant (< 5% incidence) in 3–4 years of field screenings. Of the 61 genotypes tested, 21 were free from downy mildew, 14 had less than 5% incidence, and the rest showed variable susceptible reactions. Therefore, the technique can be reliably and effectively used in the greenhouse to detect disease escapes and to indentify resistance.     

A single recessive gene for stem sweetness in sorghum

Summary The inheritance of stemsweetness in sorghum has followed a qualitative pattern, non-sweet being monogenically dominant over sweet. Hence sweetness was controlled by a single recessive gene. A maternal effect was not involved for the expression of sweetness.     

Environmental factors influence the expression of resistance to sorghum midge, Stenodiplosis sorghicola

Host plant resistance is an effective means of controlling sorghum midge (Stenodiplosis sorghicola). We studied the influence of environmental factors on expression of resistance to sorghum midge in three midge-resistant and two midge-susceptible genotypes. Midge-resistant lines AF 28, ICSV 197, and TAM 2566 suffered 8.8 to 17.3% damage across seven so wings compared to 25.6%damage in ICSV 112, and 69.4% damage in CSH 5. Susceptibility of the midge-resistant lines (AF 28, ICSV 197, and TAM 2566) decreased with an increase in open pan evaporation, maximum and minimum temperatures, and solar radiation; while the midge-susceptible lines (ICSV 112 and CSH 5) showed a poor interaction with these factors. Midge damage in ICSV 197 showed a negative correlation with minimum temperature and relative humidity and positive correlation with sunshine hours,while the reverse was true for CSH 5. Grain growth rate between 0 and 3 days after anthesis was lower in crops sown on 1st October, when AF 28 and ICSV 197 suffered maximum midge damage. Maximum and minimum temperatures and maximum relative humidity influenced the moisture content of the grain, grain growth rate, and sorghum midge damage. There was considerable variation in genotype × environment interaction for expression of resistance to sorghum midge,and the implications of these results have been discussed in relation to development of sorghum cultivars with resistance to this insect. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genotypic resistance in sorghum to head bug,Calocoris angustatus Lethiery

Summary Sorghum head bug, Calocoris angustatus Leth., is an important pest of grain sorghum. We screened nearly 15000 germplasm accessions for resistance to this pest between 1980 and 1990 under natural and headcage conditions. Data were recorded on bug numbers, grain damage (1 = highly resistant the 5 = highly susceptible), and seed germination. Under natural conditions, 34 genotypes suffered moderate levels of grain damage (damage rating (DR) 1.7 to 2.9) compared with a DR of 4.0 to 4.6 in the susceptible controls CSH 1, CSH 5 and CSH 9. IS 17610, IS 17645, IS 21444, IS 19948, IS 25069 and IS 19949 suffered a DR of less than three, and harbored less than 150 bugs/panicle compared with a DR of 4.3 to 4.7, and 248 to 353 bugs/panicle in the susceptible controls CSH 1, CSH 5 and CSH 9 when infested under headcage with 5 pairs of bugs/panicle. IS 18274, IS 20664, IS 20059, IS 25069, and IS 19951 had 150 to 300 bugs/panicle but suffered moderate levels of grain damage (DR less than 3), while the reverse was true in case of IS 8064, IS 19455, IS 19955, IS 20024, IS 20740, IS 23627, IS 2761, and IS 9692. During the 1989 rainy season, IS 14108, IS 17610, IS 17618, IS 17645, IS 19949, IS 19950, IS 19957, IS 20068, IS 25760, IS 27452, IS 27477 and IS 27329 suffered moderate levels of grain damage when infested with 5 and 10 pairs of bugs/panicle, and recorded more than 80% seed germination compared with a DR of 3.9 to 5.0, and seed germination of 15–18% in the susceptible controls CSH 1, CSH 5 and CSH 9. There is a considerable diversity in the genotypes resistant to head bugs, and attempts should be made to transfer the resistance into agronomically acceptable cultivars.     

Inheritance of resistance to head bugs and its interaction with grain molds in Sorghum bicolor

Sorghum head bug, Calocoris angustatus Lethiery is one of the most important pests of grain sorghum in India. Head bug damage increases the severity of grain molds, which renders the grain unfit for human consumption. Therefore, we studied the gene action for resistance to head bugs and grain molds in a diverse array of male-sterile lines and testers in a line × tester mating design under natural infestation. Mean squares for parents, parents vs crosses, lines, testers, and lines × testers were significant for head bug damage and grain mold severity. General combining ability (GCA) effects were significant and negative for ICSA 88019 for head bug damage, and ICSA 88019 and ICSA 88020 for grain molds (except for ICSA 88020 in 1993). General combining ability effects were positive for ICSA 42 and 296 A. GCA effects of lines and testers for head bug damage and grain mold severity were in the same direction (+ve or −ve). Head bug damage in the grain was significantly correlated with grain mold severity. Testers IS 8891, IS 15107, and TAM 2566 (with colored grain and less susceptibility to molds) produced mold-resistant hybrids in combination with all the male-sterile lines, while the reverse was true in the case of Swarna and ICSV 112. Resistance to head bugs showed dominance to partial dominance type of gene action, while in the case of grain molds, it showed dominance to over dominance. Resistance to these pests is governed by both additive and nonadditive types of gene action. The implications of these results are discussed in relation to need for crop improvement in sorghum. This revised version was published online in July 2006 with corrections to the Cover Date.     

Compensation in grain weight and volume in sorghum is associated with expression of resistance to sorghum midge, Stenodiplosis sorghicola

Sorghum midge, Stenodiplosis sorghicola (Coquillett) is one of the most important pests of grain sorghum worldwide. We studied the inheritance of resistance to sorghum midge and compensation in grain weight and volume in panicles of sorghum hybrids and their parents under uniform infestation (40 midges per panicle for two consecutive days). Sorghum midge damage ranged from 8.2 to 82.4% in the maintainer lines (B-lines) of the females parents (A-lines), and 9.0 to 67% in the male parents (restorer lines). Hybrids involving resistant × resistant parents were highly resistant, while those involving resistant ×susceptible and susceptible × resistant parents showed moderate susceptibility. Susceptible × susceptible hybrids were susceptible. Compensation in (percentage increase) grain weight and volume in midge-infested panicles of midge-resistant parents and their F₁ hybrids was greater than in midge-susceptible parents and hybrids. General combining ability effects for midge damage, and grain weight and volume were significant and negative for the midge-resistant females (ICSA 88019 and ICSA 88020), whereas those for the midge-susceptible females (ICSA 42 and 296A) were significant and positive. However, the reverse was true in case of compensation in grain weight and volume. Inheritance of compensation in grain weight and volume and resistance to sorghum midge is controlled by quantitative gene action with some cytoplasmic effects. Resistance is needed in both parents to realize full potential of midge-resistant hybrids. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic analysis of biotype I greenbug resistance in sorghum

The greenbug has been a major insect pest of sorghum since 1968. Although sources of genetic resistance have been identified to combat this pest, new and virulent biotypes have successfully overcome these resistance genes. KS 97 was developed and released by the Kansas Agricultural Experiment Station as a new germplasm source of biotype I greenbug resistance in sorghum. The objectives of this study were to evaluate combining ability effects for greenbug resistance in KS 97 and to determine the number of genes responsible for this trait. Six inbred lines, including KS 97 and greenbug resistant and susceptible checks, were intercrossed using a Design-II mating scheme to produce nine F1 hybrids. Responses of seedlings of parent lines and hybrids to biotype I greenbug were evaluated in replicated growth chamber experiments. The results of these studies indicated significant effects of general combining ability (GCA) and specific combining ability (SCA). Greenbug resistance derived from KS 97 was found to be incompletely dominant, and the GCA effect for resistance associated with KS 97 was superior to that associated with PI550610, the resistant check. Segregation studies to determine the number of genes responsible for greenbug resistance in KS 97 were conducted in BC1F1 populations. KS 97 was introgressed into three greenbug-susceptible genetic backgrounds. Segregation analysis indicated a consistent 1:3 (resistant:susceptible) segregation ratio for greenbug resistance across populations. The simplest explanation for these results is that two dominant genes requiring complementary gene action control resistance. This revised version was published online in August 2006 with corrections to the Cover Date.     

A test for obligate apomixis in grain sorghum R473

Summary Segregation patterns in progeny arrays of selfed plants, heterozygous for the Mdh 1 isozyme marker locus, were used in an attempt to confirm the presence of apomixis in the grain sorghum line R473. No evidence for obligate apomictic reproduction was obtained. However, our studies did not rule out the possibility of a low level of facultative apomixis in R473.     

Callus induction and plant regeneration from anther and inflorescence culture of Sorghum

Summary Twenty-five inbred lines, including grain and forage types from the USA and China, two hybrids, one Sorghum almum, and one Parasorghum (S. versicolor) were tested for their response to anther culture. Three nutrient media were effective in inducing anther calli from six cultivars (Xin White, TX 403-TSB, DDY Sommer Milo, TX 2779, Brawley, and Spur Federal) and one was effective for plant regeneration for one cultivar, Xin White. Averaged over media, callus induction frequency (number of calli per 100 anthers) was highest in cultivars Xin White and TX 403-TSB (6.7 and 3.9%, respectively). The means of cultivars for media C17-2 and Ms-t-z-2, 4.3 and 3.2%, respectively, were superior to that for medium 85D3-2 (0.1%). Expressed as an average of the six cultivars and three media the mean calli induction frequency was 2.6%; however, differential responses of genotype and medium were noted. Among the 10 regeneration media tested, medium MS-d-4 containing Murashige and Skoog basal components plus 2.0 mg/l indole-3-acetic acid (IAA) and 2.5 mg/l kinetin was the most effective for plant regeneration. Numbers of albino plants and calli developing only roots increased directly with callus-induction time, whereas the frequency of plant regeneration decreased. Regenerated plants had varied numbers of chromosomes in root tip cells: 10, 15, 20, 40, and 60. The 29 regenerated plants that reached maturity, however, were highly fertile and contained only 10 bivalents in pollen mother cells. Normal chromosome number and behavior for the regenerated plants suggest that induced calli originated from cells other than microspores. However, spontaneous chromosome doubling in microspore-derived haploids may occur. The appearance of albinos also implies that haploids may have been produced from anther culture.Joint contribution of the Dept. of Agronomy and USDA-ARS, Kansas Agricultural Experiment Station, Manhattan, KS 66506-5501, USA. Contribution no. 88-566-J.