FACTORS AFFECTING INFECTION GRADIENTS FROM A POINT SOURCE OF PUCCINIA POLYSORA IN A PLOT OF ZEA MAYS

Two plots of Zea mays were planted in April and September, respectively, at Ibadan, Nigeria during 1956. A point source of inoculum consisting of potted maize plants heavily infected with the American corn rust, Puccinia polysora Underw., was introduced at pre-arranged times before the plots became naturally infected. Disease gradients from these point sources of infection were assessed by the number of pustules subsequently appearing on plants along the circumferences of concentric circles around the source of infection. 'Control' plots were planted at the same time as the main trial and the pattern of natural infection was observed in an attempt to assess the degree of contamination in the main experiment.
In the centre of the main experiment a volumetric spore trap gave continuous records of the uredospore content of the atmosphere immediately above the crop during both plantings for periods of 2 weeks before planting until 2 weeks after the last assessment of infection.
The forms of the disease gradients were considerably altered by several factors—principally contamination by inoculum from outside sources, the method of assessment and the time at which the assessments were made.     

玉米原生质体的植株再生

以玉米花粉诱导产生的胚性愈伤组织,在 N6基本培养基附加激动素2 mg/l,6-苄基氨基嘌呤1mg/l,2,4-D 0.3 mg/l,水解酪蛋白500 mg*l 及谷酰胺250 mg/l 的培养基上进行转代培养。用转代培养一年半后的胚性愈伤组织分离原生质体,原生质体培养在附加激动素0.2 mg/l,6-苄基氨基嘌呤0.1 mg/l,2,4-D 0.5 mg/1,水解酪蛋白200 mg/l,谷酰胺100 mg/l及椰乳296的原生质体培养基 Z_2中。培养4—6天后,原生质体的再生细胞进行第一次分裂;培养3星期后发育成肉眼可见的小愈伤组织。此后,需添加降低糖浓度的同样原生质体培养基 Z_2共两次。待再生愈伤组织长到直径2—4 mm 大小时,把它们先后转经第一及第二(即Z_3及 Z_4)分化培养基上诱导器官分化。最后在 Z_4分化培养基上同时有胚状体的发生及植株的分化。     

STARCH GRANULE FORMATION IN DEVELOPING SEEDS OF PISUM SATIVUM L.: EFFECT OF GENOTYPE

Cell development and starch granule formation in seeds of three pea (Pisum sativum L.) genotypes, R/R Rb/Rb, r/r Rb/Rb, and R/R rb/rb, affecting cotyledon starch were compared. Cotyledon cells at 10 days after flowering were highly vacuolated and contained small protein bodies in the vacuoles and small oval starch granules in the cytoplasm in all three genotypes. Gradients of cell development from the center to the periphery of the cotyledon and toward the cotyledon-hypocotyl axis persisted through the cell enlargement, reserve synthesis, and into the maturation stages of cotyledon development. By 14 days after flowering, many small vacuoles lined with protein deposits had been formed. Vacuoles were only observed in peripheral and basal cells by 18 days after flowering. Starch granules were oval and birefringent in all three genotypes at 10 days. Starch granules in R/R Rb/Rb and R/R rb/rb cotyledons expanded regularly remaining nearly oval and birefringent throughout development. In contrast, starch granules from r/r Rb/Rb cotyledons began to fragment by 14 days after flowering. This process began as a single fissure, followed by a second fissure usually at or near right angles. Finally, because of the fragmentation, the granules appeared compound, and only a portion of the granule was birefringent. All genotypes contained nearly equal volumes of liquid endosperm and embryo at 10 days after flowering. In addition, a layer of parenchyma tissue (ovular and/or endospermic) inside the seed coat was observed. Although, thin walled and poorly defined cytologically, the parenchyma cells contained large numbers of starch granules. These granules were a mixture of simple and compound types in all genotypes. By 18 days after flowering, the parenchyma tissue was reduced to a small layer of cell walls and all starch granules had been mobilized.     

INFLORESCENCE DEVELOPMENT IN TWO ANNUAL TEOSINTES: ZEA MAYS SUBSP. MEXICANA AND Z. MAYS SUBSP. PARVIGLUMIS

The ontogeny of tassels and ears in two annual Mexican teosintes, Zea mays subsp. mexicana and Z. mays subsp. parviglumis, was examined using scanning electron microscopy and light microscopy. Ear development in these annual teosintes follows a pattern previously described as leading to the bisexual mixed inflorescence in Z. diploperennis. Common bud primordia are initiated in the axils of distichously arranged bracts along the ear axis. These common primordia bifurcate to form paired sessile and pedicellate spikelet primordia. Development of pedicellate spikelets is arrested leaving the sessile spikelets, along with the adjoining rachis segment, to form solitary grains enclosed within cupulate fruitcases. Development of the central tassel spike is similar to that previously described in the Z. diploperennis tassel, except that the first formed axillary bud primordia form precocious tassel branches. The origin of these tassel branches suggests a possible mechanism for the transition from a distichous spike, characteristic of teosinte, to a polystichous spike, typical of maize.     

OCCURRENCE OF A STELAR LESION DURING IMBIBITIONAL CHILLING OF ZEA MAYS L.

Radicle growth of the corn inbred Oh51A was reduced by imbibitional chilling at 5 C. The effect was mediated by the initial moisture of the kernel prior to hydration. Five percent initial moisture kernels were injured while 13% initial moisture kernels were not. The formation of a structural lesion in the radicle during the first 24 hr of hydration at 5 C of 5% initial moisture kernels was correlated with subsequent radicle growth reduction at 25 C. The lesion did not form during hydration of 13% initial moisture kernels at 5 C, in kernels hydrated at 25 C, in unimbibed kernels, or in heat-killed, cold-imbibed kernels. The lesion also did not appear during the imbibitional chilling of the corn inbred B8 which did not exhibit radicle growth reduction. Two sources of Oh51A with similar lesion frequencies were different in the severity of growth reduction. While the lesion became sealed at 25 C subsequent to cold hydration, growth reduction differences were not fully explained by this phenomenon. In one source more seedlings exhibited reduced growth than expected from the frequency of observable lesions. Therefore, other types of damage contributed to the reduction of radicle growth.     

PHYTOREMEDIATION POTENTIAL OF MAIZE (ZEA MAYS L.) IN CO-CONTAMINATED SOILS WITH PENTACHLOROPHENOL AND CADMIUM

The ubiquitous coexistence of heavy metals and organic contaminants was increased in the polluted soil and phytoremediation as a remedial technology and management option is recommended to solve the problems of co-contamination. Growth of Zea mays L and pollutant removal ability may be influenced by interactions among mixed pollutants. Pot–culture experiments were conduced to investigate the single and interactive effect of cadmium (Cd) and pentachlorophenol (PCP) on growth of Zea mays L, PCP, and Cd removal from soil. Growth response of Zea mays L is considerably influenced by interaction of Cd and PCP, significantly declining with either Cd or PCP additions. The dissipation of PCP in soils was notably affected by interactions of Cd, PCP, and plant presence or absence. At the Pentachlorophenol in both planted and non-planted soil was greatly decreased at the end of the 10-week culture, accounting for 16–20% of initial extractable concentrations in non-planted soil and 9–14% in planted soil. With the increment of Cd level, residual pentachlorophenol in the planted soil tended to increase. The pentachlorophenol residual in the presence of high concentration of Cd was even higher in the planted soil than that in the non-planted soil.     

ORGAN INITIATION AND THE DEVELOPMENT OF UNISEXUAL FLOWERS IN THE TASSEL AND EAR OF ZEA MAYS

The development of the unisexual male and female flowers of Zea mays from bisexual initials in both tassels and ears has been reinvestigated with SEM and TEM. The early stages of spikelet branch primordia, spikelet initiation, and early flower development are similar in both flowers, though differences in rates of growth of glumes, lemmas, and palea were detected. In both tassel and ear flowers, a pair of stamens arises opposite the lemmas and a third stamen initiates later at right angles to the first pair but from a point on the meristem below its insertion. Gynoecia develop on both tassel and ear flowers first as a ridge which overgrows the apical meristem giving rise to the stylar canal and the elongate silk. Male flowers arise in the tassel through selective vacuolation and abortion of the cells of the early gynoecium. The single female flower in each ear spikelet arises through the vacuolation and abortion of stamens in the upper flower and the repression of growth of and the eventual regression of the lower flower in each spikelet. The significance of these selective organ abortions for practical applications is discussed.     

TAXONOMY OF ZEA (GRAMINEAE). II. SUBSPECIFIC CATEGORIES IN THE ZEA MAYS COMPLEX AND A GENERIC SYNOPSIS

A compromise classification of the genus Zea, reflecting both phylogeny and practical needs, recognizes six taxa, as follows: Section Luxuriantes : Zea perennis. Zea diploperennis, Zea luxurians. Section Zea : Zea mays ssp. mexicana (Neo-volcanic Plateau), Zea mays ssp. parviglumis Iltis & Doebley ssp. n. var. parviglumis (Rio Balsas drainage, Pacific slope from Guerrero to Jalisco), Zea mexicana ssp. parviglumis var. huehuetenangensis Iltis & Doebley var. n. (Pacific slope, western Guatemala, Prov. Huehuetenango), Zea mays ssp. mays. The new subspecies is distinguished by smaller spikelets and rachis joints, the varieties by different habitats, blooming dates and their genetic behavior in relation to cultivated Zea mays. Zea mays ssp. mexicana is the ancestor of corn.     

北京地区大葱和玉米根际VA菌根的季节变化及其与环境因子之间的关系

1986-1987年连续两年系统调查了北京地区大葱(Allium fistulosum L.)和玉米(Zeamays L.)根际 VA 菌根侵染百分率及菌根真菌孢子密度的季节变化。分析了菌根和菌根真菌的发生与几种土壤因子(土壤硝态氮、铵态氮、速效磷和有机质含量,土壤 pH 值)和气候因子(气温、积温、土温、光照、降水量,相对湿度等)之间的关系。结果表明:大葱和玉米的侵染百分率随作物生育期的增长而增加,并以6月和9月的增长速度最快。一年中,植物根际菌根真菌的孢子密度有二个高峰,分别在6-7月和10月。在北京的同一地区,一年中,几种测定的土壤因子变化很小,因此,认为气候因子对菌根发生的季节变化具有更大的影响。用线性相关和关联度分析的结果表明:一年中,菌根的发生与积温的关系最为密切。     

THE EFFECTS OF GENOTYPE AND PLOIDY LEVEL ON POLLEN SURFACE SCULPTURING IN MAIZE (ZEA MAYS L.)

Pollen exine sculpturing is a consistent feature of seed plant taxa, yet no mechanism for control of sculpturing pattern has been found. On grass pollen, exine sculpturing takes the form of closely packed spinules. Exine spinules on pollen grains from six maize populations representing all combinations of three genetic backgrounds (single cross hybrids W22 W23, N6 W23, R75 W23) and two ploidy levels (2x, 4x) were examined by scanning electron microscopy. Doubling ploidy levels from 2x to 4x increased pollen diameter (minor axis) with the magnitude of increase related to genetic background. For spinule density, only the effect of genetic background was statistically significant. Spinule density was altered by the genotype of the plant on which the pollen was produced but not by the ploidy level, including genome number and difference in surface area and cytoplasmic volume resulting from chromosome doubling.