Effect Of Plant Age Research Articles

Effect of plant age, leaf age and leaf position on infection of carrot leaves by Cercospora carotae

A greenhouse study was conducted to determine the effects of plant age, leaf age and leaf position on infection of carrot (Daucus carota var. sativa) by Cercospora carotae. Infection was quantified as the number of lesions cm-2 of leaf surface and the length of incubation period. The relative number of lesions decreased linearly with increasing plant age from 39- to 60-d-old plants, and remained low from 60- to 71-d-old plants. The incubation period increased from 9.0 to 16.6 d, with increasing plant age. Relative number of lesions decreased with increasing leaf age from 1 to 36 d, but the variation among leaves was high. The incubation period increased from 9.0 to 18.3 d with increasing leaf age, but lesions on a few young leaves appeared relatively late. Generally, differences in relative number of lesions for leaves on different positions for 10- and 13-wk-old plants were not significant. Infection on all leaves except the two youngest was representative of infection on whole plant. Effect of leaf position on incubation period was different for the 10- and 13-wk-old plants and for the two trials. Plants younger than 60 d old, in the seven-to eight-leaf stages should be used for experiments on the initial development of Cercospora blight of carrots.

Influence of plant age, whitefly population and cultivar resistance on infection of cotton plants by cotton leaf curl virus (CLCuV) in Pakistan

The effect of plant age, the whitefly Bemisia tabaci population levels, and cultivar resistance to cotton leaf curl virus disease was determined for 10 newly developed mutant lines (via radiation) and one resistant and two susceptible/tolerant control varieties, under natural inoculation by the vector whiteflies. All cotton mutant lines/varieties become increasingly resistant to CLCuV as plants aged. Expression of the age-related resistance to CLCuV infection was more apparent in late growth stages. Maximum increase in % disease incidence occurred at 6 weeks. There was no significant correlation of whitefly levels with % disease incidence and only small differences in whitefly population levels for all mutant lines/varieties. None of the test lines/varieties under field or graft inoculation conditions were immune. All mutant lines including negative and positive controls were symptomatic but differed in their response to CLCuV. Six mutant lines, namely NIAB-103, NIAB-101, NIAB-998, NIAB-358, NIAB-98 and the negative control CIM-443 showed highly resistance responses while NIAB-78 and S-12 were highly susceptible. Similar results for disease reaction were obtained when test mutant lines were graft inoculated under net-house conditions (insect free conditions) except for CIM-443, which was resistant. Present results suggested that there is evidence that source of resistance against CLCuV is available in several of the tested mutant lines. These lines may be released as CLCuV resistant varieties or their resistance could be incorporated into other commercial cultivars to manage leaf curl disease. The current study furthered our knowledge about the epidemiology of CLCuV for improved forecasting to manage the disease and identified useful resistant materials.

Survival of native plants of Hawkesbury Sandstone communities with additional nutrients: effect of plant age and habitat

Australian soils are naturally low in nutrient concentrations, particularly nitrogen (N) and phosphorus (P). Native plants are well adapted to low-nutrient soils, and can be adversely affected when exposed to higher concentrations of nutrients. The Hawkesbury Sandstone soils in northern Sydney are naturally low in nutrients, but often receive additional nutrient input from urban stormwater run-off. Increases in soil nutrients in urban bushland are associated with the presence of exotic species, and the decline in the diversity of native species. This study tested the hypothesis that high concentrations of nutrients, in particular P, in the disturbed soils of urban bushland, reduce survival of native plants. We examined the survival of native species under five different nutrient concentrations that are typical of nutrient-enriched urban bushland soil, in two glasshouse experiments. The experiments examined both survival of seedlings and survival of 6-month-old plants. We used native species that are adapted to both nutrient-poor and nutrient-rich soils. In general, the survival of native plants decreased with increasing nutrient concentrations. At soil total-P concentrations >200 mg kg–1, most plants died. Seedlings were more sensitive to added nutrients than the 6-month-old plants. Species that were from higher-nutrient soil had consistently higher survival than species from low-nutrient soils, under the nutrient addition treatments. These results suggest that at high soil nutrient concentrations typical of stormwater-affected urban bushland, native plant species of low-nutrient soils will be unable to survive. If ecological restoration works are to be done in such areas, replanting with more mature plants from naturally high-nutrient habitats is likely to be the most successful. However, restoration of these areas may have limited success and they are likely to remain dominated by exotic plant species.

Effects of Plant Age, Leaf Position, Inoculum Density, and Wetness Period on Bipolaris coicis Infection in Adlays of Differing Resistance.

The effects of plant age, leaf position, inoculum density, and wetness period on the development of adlay leaf blight caused by Bipolaris coicis were evaluated using six adlay cultivars or lines of differing resistance in field plots and in the greenhouse. Levels of resistance to leaf blight among the six cultivars or lines were consistent between the 1998 and 1999 field experiments. With the aging of adlay plants, leaf blight development gradually increased in all cultivars or lines tested. Leaf blight severity was significantly greater on the lower (older) leaves than on the upper (younger) leaves. As inoculum density increased from 103 to 106 conidia per ml, the development of leaf blight increased. Disease severity also increased as the time of leaf wetness duration increased from 0 to 60 h. Wetness duration above 48 h and a high inoculum density at 106 conidia per ml caused severe leaf blight symptoms in adlay seedlings. The data from the greenhouse experiments consistently revealed the same trends in relative levels of susceptibility of adlay cultivars to leaf blight as those seen at late plant growth stages under field conditions.

Leaf Position Prevails Over Plant Age and Leaf Age in Reflecting Resistance to Late Blight in Potato

ABSTRACT The effects of plant age, leaf age, and leaf position on race-nonspecific resistance against Phytophthora infestans were investigated in a series of field and controlled environment experiments with five different potato (Solanum tuberosum) cultivars. Leaf position proved to be the most significant factor; apical leaves were far more resistant to late blight than basal leaves. Plant age and leaf age had only minor effects; therefore, the resistance of a specific leaf remained about the same during its entire lifetime. The gradual increase in late blight resistance from basal leaves to apical leaves appeared to be a general effect, irrespective of cultivar, growing conditions, or resistance test. Therefore, it is important to consider leaf position in tests for late blight resistance, because contrasts in resistance may be ascribed erroneously to differences between genotypes or treatments, whereas they are actually caused by differences in leaf position.

Acute drought stress and plant age effects on alkamide and phenolic acid content in purple coneflower roots.

The effects of acute periods of drought stress on dry weight, and alkamide and phenolic acid content in purple coneflower [Echinacea purpurea (L.) Moench, Asteraceae] roots are described. Plants subjected to brief drought stress periods for two seasons during the initial flowering stage (D-F2) produced fall-harvested roots with significantly greater cichoric acid concentration (mg/g) than corresponding well-watered controls of the same age (C-2). Total alkamide, including the tetraenoic acid isomers, and chlorogenic acid concentrations from fall-harvested roots were largely unaffected by drought stress, regardless of when the stress occurred developmentally. The alkamide concentration in three-year roots was significantly less than that in two-year roots, with an average decrease of 50.5 %. Conversely, total phenolic acids increased an average of 67.1 % for all treatments from two to three years of age. Root dry weight increased significantly by an average of 70.0 % for all drought-stressed plants from two to three years of age, compared to an increase of 35.2 % for well-watered controls. The results suggest that controlled drought stress can stimulate increased root dry weight and root cichoric acid content, and that root age is the predominant factor determining overall phytochemical content variation.

Effect of plant age and cottony snow mold on winter survival of forage grasses

The low temperature basidiomycete (LTB, syn. Copribus psychromorbidus Traquair), the causal agent of cottony snow mold, is a major constraint to forage grass survival and productivity in the parkland region of the Canadian prairies under prolonged snow cover (e.g., 160 d). Studies were conducted to establish the level of the snow mold resistance in seven grass species commonly grown in western Canada and to identify the seeding dates that permit grass plants to develop maximum levels of resistance to snow mold. Following attack by the LTB fungus, considerable variation in winter survival and forage yield was observed among the grass species. Smooth brome and meadow brome were most resistant, followed by timothy and creeping red fescue. Tall fescue and orchardgrass were the most susceptible. Controlled-environment and field studies demonstrated that orchardgrass seeded in late spring resulted in greater winter survival and dry matter yield than when seeded in July or August, both in snow mold inoculated and noninoculated treatments. Additional mortality and dry matter yield loss were linked to snow mold injury. These results demonstrated that snow mold injury could reduce winter survival and yield in first-year forage grasses, especially in orchardgrass, and early seeding could reduce the impact of winter stresses. Key words: Grass, orchardgrass, timothy, smooth bromegrass, meadow bromegrass, creeping red fescue

Níveis críticos de fósforo no solo e na planta para gramíneas forrageiras tropicais, em diferentes idades

Dois experimentos foram realizados simultaneamente, em casa de vegetação, para avaliar os efeitos da idade das plantas e de períodos de rebrotação sobre os valores dos níveis críticos de fósforo no solo e na planta para duas gramíneas forrageiras tropicais. Os tratamentos corresponderam aos arranjos fatoriais 2x5x5, no estudo de crescimento inicial, e 2x2x5, no estudo de rebrotação. Os fatoriais consistiram de duas espécies (Brachiaria decumbens cv. Basilisk e Panicum maximum cv. Mombaça); cinco idades (14, 28, 42, 56 e 70dias após a emergência), durante o crescimento inicial e em dois períodos do estudo da rebrotação (28 e 42dias) após um crescimento inicial de 42dias, e cinco doses de fósforo (0, 64, 128, 320 e 640mgdm-3). Os tratamentos, com três repetições, foram distribuídos em blocos ao acaso. Nos ensaios, utilizou-se amostra de Latossolo Vermelho-Amarelo. Para determinação dos teores de fósforo disponível no solo, foi utilizado o extrator Mehlich-1. Os níveis críticos (NíCrí) de fósforo no solo para B. decumbens foram maiores do que para P. maximum Os NíCrí no solo decresceram exponencialmente com a idade das plantas de 95,1 e 75,6mgdm-3, aos 14dias, para 38,1 e 28,4mgdm-3, aos 70dias, com relação a B. decumbens e P. maximum, respectivamente. Na fase de rebrotação, os NíCrí no solo foram semelhantes nos dois períodos, com valores próximos aos estimados para as plantas aos 70dias. Os NíCrí de fósforo na parte aérea das plantas decresceram exponencialmente de 0,57 e 0,60dagkg-1, aos 14dias, para 0,08 e 0,07dagkg-1, aos 70 dias, com relação a B. decumbens e P. maximum, respectivamente. B. decumbens apresentou maiores valores de NíCrí de fósforo na parte aérea das plantas, exceto na idade de 14dias. Na fase de rebrotação, os NíCrí na parte aérea foram maiores aos 28dias, diminuindo, aos 42dias, para valores similares aos estimados nas idades de 56 e 70dias, no crescimento inicial. Assim, para avaliação criteriosa do estado nutricional da planta em termos de fósforo e recomendação de fertilização, recomenda-se considerar a idade das plantas após o plantio da forrageira e a cada ciclo de crescimento.

Effect of plant age on resistance to Ascochyta rabiei in chickpea

The impact of plant age on resistance to ascochyta blight of chickpea (Cicer arietinum) was assessed on kabuli cvs. UC27 (susceptible) and Sanford and B90 (partially resistant) and desi cv. Myles (partially resistant) using two isolates of Ascochyta rabiei. Tests were conducted under controlled conditions and in field trials in 1999 and 2000. Seed was sown at regular intervals to produce plants at different growth stages (seedling, vegetative, flowering, podding), which were all inoculated at the same time in randomized complete block experiments with four replications. Cultivar UC27 was highly susceptible at all stages of plant development. However, plant age had a large impact on the reaction of resistant cultivars to A. rabiei. In growth chamber studies, blight severity was low in seedlings of the resistant cultivars (range, 4-20%) and highest in podding plants (41-82%) 2 weeks after inoculation. In the field trials, severity at 2 weeks after inoculation showed a similar pattern, with mean severity among resistant cultivars ranging from 1 to 2% in seedlings and 3 to 28% in podding plants. Severity at 8 weeks after inoculation on plants of resistant cultivars inoculated as seedlings was low (6-14% in 1999, 10-23% in 2000) relative to those inoculated at podding (65-91% in 1999; 54-83% in 2000) in the field trials. These results indicate that resistance decreases with plant age in the partially resistant chickpea cultivars adapted to western Canada and that resistance alone may not provide adequate disease control.

The effect of plant age and soil amendments on severity of phytophthora root rot of pepper (Capsicum annuum L) in South Western Nigeria

The incidence and severity of pepper Capsicum annuum to phytophthora root rot caused by Phytophthora infestan in Southwestern Nigeria was investigated. Root rot incidence and severity was significantly reduced with increase in the plant age. The highest level of root rot, of 81.7% and 67.6% obtained in 4 and 6 weeks old pepper plants were reduced to 25% and 5% in 10 and 12 weeks old pepper plants respectively. The resistance of the pepper plant to root rot severity increased with age. The result also showed that amendments of the soil with chicken manure wood ash and neem leaf suppressed the root rot incidence and severity of disease in the pepper plant.

Effect of plant age on water content in crowns of fall rye and winter wheat cultivars differing in snow mold resistance

Resistance to snow molds in winter wheat increases with plant age, and older plants express higher levels of resistance than young plants. Experiments were conducted to study the effect of plant age on percent crown water content (%CWC) and dry weights in fall rye and winter wheat cultivars grown under controlled environments and in the field at Lethbridge, AB. Under controlled environments, the oldest (6 wk of pre-hardening growth at 20°C) treatments accumulated the greatest dry weights following exposure of plants to 1 to 6 wk hardening conditions at 2°C, compared with younger (1 to 4 wk pre-hardening growth) treatments. Exposure of plants to hardening temperatures had the greatest effect on %CWC values, which decreased, gradually, from 82–89% (4.95–8.67 g H2O g–1 DW) in unhardened treatments to 67–72% (2.05–2.65 g H2O g–1 DW) in plants receiving the 6 wk pre-hardening and 6 wk hardening growth. However, the oldest treatments (4 to 6 wk pre-hardening growth) always exhibited the lowest %CWC values among all hardening treatments. The %CWC in the oldest (6 wk) unhardened plants was also lower ([Formula: see text] = 80.8% or 4.24 g H2O g–1 DW) than in the youngest (1wk) unhardened plants ([Formula: see text] = 91.2% or 11.31 g H2O g–1 DW ), demonstrating that water loss occurs in older plants in the absence of low hardening temperatures. In a field study at Lethbridge during the autumn, winter, and early spring of 1997–1998 and 1998–1999, different seeding dates were employed to obtain plants differing in age and developmental state. The %CWC in early-seeded treatments was lower during the autumn, and remained lower in early spring, compared with later seeded cultivars. The %CWC in crowns was negatively associated with the snow mold resistance rating of a fall rye and five winter wheat cultivars under controlled environment conditions, and among a fall rye and 13 winter wheat cultivars in the field; the highest correlation values in the field were observed from mid-November to mid-March during 1997–1998 (r = –0.84), and 1998–1999 (r = – 0.76). These results indicate that the type of snow mold resistance that increases with plant age is related to the accumulation of crown dry matter and the ability of wheat and rye plants to lose crown water in response to both extended growth at warm temperatures and hardening at low, above freezing temperatures. Key words: Carbohydrates, fructans, low temperature basidiomycete, Coprinus psychromorbidus

Effect of plant variety, plant age and photoperiod on glandular pubescence and host‐plant resistance to potato moth (Phthorimaea operculella) in Lycopersicon spp.

SummaryThe effect of plant age and daylength on glandular pubescence was determined for two lines of tomato derived from Lycopersicon hirsutum (BTN 979 and LA 1777A) and a variety of L. esculentum (N 91‐1‐1‐1‐1). Densities of type I, IV, VI and VII glandular trichomes were lowest in N 91‐1‐1‐1‐1 and, over all varieties, were more dense on plants aged greater than 6 wk. Daylength interacted with variety to significantly affect densities of type VII trichomes only. Host‐plant resistance to Phthorimaea operculella was determined in preliminary tests using insects cultured from founders from a potato crop and in confirmatory tests using (less readily available) insects recovered from foliage of a tomato crop. Mortality of ex‐potato neonates on LA 1777 A and BTN 979 foliage was higher 18 h after placement than for N 91‐1‐1‐1‐1, with no effect of day length or plant age. Mortality for ex‐tomato neonates followed a similar trend. Ten days later, two‐thirds of ex‐tomato larvae had established mines on N 91‐1‐1‐1‐1 but fewer (16.7%) were live on other varieties. Stepwise multiple regression using variety as the sole factor was significant (P<0.001) in accounting for 61.4% of the variation in ex‐tomato larval survival but addition of other factors to the regression model was not significant. BTN 979 supported fewer, smaller adults to develop than did N 91‐1‐1‐1‐1, whilst no adults developed on LA 1777 A. In a non‐choice test using ex‐potato adults, significantly more eggs were laid on N 91‐1‐1‐1‐1 than on L. hirsutum varieties and 9‐wk‐old plants were preferred over plants three weeks older or younger. The same variety and plant age trends were evident in a free‐choice test using ex‐tomato adults.

Conservation requirements of an exploited wildflower: modelling the effects of plant age, growing conditions and harvesting intensity

When flowers are harvested from wild plants an issue for conservation managers is whether sufficient seeds remain for population replacement, especially if it is subject to recurrent disturbance. Field data on the effect of flower picking on seed availability over 13 years were available for the most heavily exploited wildflower in Australia, Banksia hookeriana, a fire-killed shrub restricted to a 2000 km 2 area in the northern sandplains of southwestern Australia. These were combined with demographic data from 14 long-term monitoring plots scattered over the landscape. Growing conditions were termed ‘good’ to ‘poor’ depending on how they affected the number of inflorescences produced, and recruitment of young plants. A computer model was developed based on best-fit equations for all key processes accounting for seed and seedling production and loss. The model indicates that self-replacement (maintenance of a stable population size at a given age from one generation to the next) is unlikely for the first 5–11 years following fire, depending on growing conditions, even in the absence of picking. Picking has little effect on the minimum fire interval for self-replacement under good growing conditions, but, under poor conditions, minimum fire interval rises from 12 years at 0% picking to 20 years at 30% picking. Miscalculation of the intensity of picking allowable could have serious consequences for conservation of wild populations, as fires are most likely at 10–20 year intervals. A second computer model took inter-fire establishment into account. It gave similar results for self-replacement conditions, but also indicated that the level of picking that could be sustained diminishes sharply once fires occur at intervals >20 years. We suggest caution be exercised by conservation authorities in setting the age to first picking and the levels of picking permitted for wild populations of Banksia hookeriana. Our models are suitable for a wide range of vulnerable, fire-killed species at present harvested from the wild.

Species richness and fluctuation of defoliator Lepidoptera populations in Brazilian plantations of Eucalyptus grandis as affected by plant age and weather factors

The effect of plant age and weather factors on species richness and fluctuation of defoliator Lepidoptera populations was investigated in a Eucalyptus grandis plantation subjected to a five-year survey (June 1993–July 1998) in Santa Bárbara County, State of Minas Gerais, Brazil. Adult Lepidoptera were collected every 15 days with five light traps, and the number of individuals per morphospecies in each site was recorded. Lowest numbers of individuals were obtained in July (14.4 ± 4.7 insects/trap) and highest numbers were obtained by late December (86.8 ± 41.1 insects/trap). During the five-year period, 653 species of Lepidoptera were collected and the Geometridae Stenalcidia grosica, Glena unipennaria, and Oxydia vesulia were the most abundant species. The mean seasonal fluctuation of the first two species were positively correlated with the total Lepidoptera fluctuation ( p < 0.01; r = 0.6; n = 98), unlike the third species (i.e. O. vesulia) which was poorly correlated with the total fluctuation ( p = 0.05; r = 0.2; n = 98). Multiple regression models were developed to assess the relative importance of plant age and weather factors (temperature, relative humidity, and rainfall) affecting species richness and fluctuation of Lepidoptera populations. Plant age and average temperature were the main weather factors affecting species richness and abundance of total individuals and individuals of the species S. grosica. Older plants (six- to seven-years old) and lower temperatures (≈18°C) seem to favor species richness and higher populations of Lepidoptera, especially S. grosica. In contrast, plant age and rainfall were the main factors affecting the fluctuation of G. unipennaria populations which presented higher incidence in older plants (six- to seven-years old) and higher rainfall (≈400 mm). We were unable to develop robust models for fluctuation of O. vesulia populations ( r 2 < 0.15). The obtained results suggest that high populations of the main defoliator Lepidoptera species present in the area are more likely to occur in plants older than five years and especially during the rainy season (October–March).

Impact of a disease and a defoliating insect on houndstongue (Cynoglossum officinale) growth: implications for weed biological control

Summary The noxious weed houndstongue (Cynoglossum officinale) has become a major problem on the forested rangelands in the interior of British Columbia. However, recently the fungus Phoma pomorum and the ranchman's tigermoth (Platyprepia virginalis) were identified as potential biocontrol agents of this biennial weed. Infection by the fungus Ph. pomorum resulted in the formation of large brown lesions on leaves of houndstongue. In culture, the fungus readily produced pycnidia with pycnidiospores measuring 5.7 μm × 1.7 μm. The effect of Ph. pomorum and P. virginalis on the growth of houndstongue was examined over a six week period. Leaf age strongly influenced the intra plant distribution of insect feeding and lesion formation with Ph. pomorum primarily attacking the older leaves, while P. virginalis larvae preferred feeding on young leaves. Infection of leaves by Ph. pomorum resulted in their premature death. The effect of infection by Ph. pomorum on plant weight varied among tests, but the disease usually increased the number or percentage of dead leaves and reduced root biomass. A study of the effect of plant age and disease on houndstongue showed that younger plants infected with Ph. pomorum had a slightly higher percentage of dead leaves than older plants, but that reductions in live leaf weight and root weight were similar for different age groups. Six weeks after exposure to feeding damage by P. virginalis, there was no significant effect of P. virginalis on plant weight either acting alone or in combination with Ph. pomorum.

The Effect of Plant Age on Taxane Content of Cultivated Taxus

ABSTRACT The relative content of taxol and taxanes in rooted cuttings (˜ 1 year old), liner (3–4 years old), and landscape-size (7–8 years old) Taxus plants was investigated. Leaves contained a higher concentration of paclitaxel and taxanes than other plant tissues. The concentration of taxanes in the stems was relatively small and resulted in dilution of the taxanes in the whole plant biomass of liner and landscape-size plants. The small size of rooted cuttings (average dry weight = 0.94 g/plant) and liners (average dry weight = 39 g/plant) meant separation of leaves from stems and roots would not be practical. For the rooted cuttings, no substantial reduction in the paclitaxel/taxanes concentration resulted from extracting the whole plants versus leaves.

Effect of plant age, larval age, and fertilizer treatment on resistance of a cry1Ab-transformed aromatic rice to lepidopterous stem borers and foliage feeders.

The resistance of vegetative, booting, and flowering stage plants of a variety of an aromatic rice, Oryza sativa L., transformed with a Bacillus thuringiensis Berliner cry1Ab gene under control of the maize phosphoenolpyruvate carboxylase (PEPC) promoter was evaluated against four lepidopterous rice pests--the stem borers Chilo suppressalis (Walker) (Lepidoptera: Crambidae) and Scirpophaga incertulas (Walker) (Lepidoptera: Pyralidae), and the foliage feeders Cnaphalocrocis medinalis Guenée (Lepidoptera: Pyralidae) and Naranga aenescens Moore (Lepidoptera: Noctuidae). Plants of the cry1Ab-transformed line (no. 827) were more resistant to young larvae of S. incertulas, C. suppressalis, and C. medinalis than control plants at the vegetative stage but not at the flowering stage. Survival of 10-d-old stem borer larvae did not differ on cry1Ab plants and control plants at either the vegetative or flowering stage, but the development of 10-d-old C. suppressalis larvae was retarded on the vegetative stage cry1Ab plants. Immunological analysis also showed an apparent decline in Cry1Ab titer in leaf blades and leaf sheaths at the reproductive stage. In experiments comparing three fertilizer treatments (NPK, PK, and none), there was a significant interaction between fertilizer treatment and variety on larval survival only in whole-plant assays at booting stage with C. suppressalis. On cry1Ab plants, larval survival did not differ significantly among the three fertilizer levels, whereas on control plants survival was highest with the NPK treatment. cry1Ab plants tested at the sixth and seventh generations after transformation were more resistant than control plants to N. aenescens and C. suppressalis, respectively, suggesting that gene silencing will not occur in line 827. The results of the experiments are discussed in terms of resistance management for B. thuringiensis toxins in rice.

Root age and phosphorus effects on colonization of Andropogon gerardii by mycorrhizal fungi

We examined the effects of plant age and root age on mycorrhizal colonization in the obligate mycotrophic grass Andropogon gerardii grown at high and low rates of soil phosphorus availability. There were significant interactions between soil P availability, plant age, root age and mycorrhizal colonization. Mycorrhizal colonization of 1-week-old roots increased with plant age, but was not significantly affected by soil P availability. Colonization of roots increased significantly with increasing root age only in the low-P treatment. Although the high-P treatment increased rates of root extension for some root age classes, there were not consistently lower rates of colonization in these roots. Studies of P acquisition by A. gerardii and other mycotrophic plants should take these interacting factors into account, especially when examining exploitation of nutrient-enriched patches.

Severity of Alternaria Leaf Spot and Seed Infection by Alternaria sesami (Kawamura) Mohanty and Behera, as Affected by Plant Age of Sesame (Sesamum indicum L.)

AbstractAlternaria leaf spot incited by Alternaria sesami, was monitored to determine the effect of plant age on disease severity and seed infection by A. sesami in plots containing sesame accession SPS SIK 110 plants of five different ages. The increase in percentage leaf area blighted and percentage defoliation fit the Gompertz model more closely than the logistic model. Rates of increase in blighted leaf area and defoliation, and areas under disease curves (AUDPC) varied among the five different plant ages. Plant ages with larger AUDPCs generally had faster rates of disease progress. Plants inoculated at 8 and 12 weeks of age were most susceptible to the disease and those inoculated at 4 weeks exhibited the least susceptibility. Seed infection was determined by the oat‐meal agar plate method and the infection was highest in plants infected at 8 and 10 weeks of age and least in plants infected at 4, 6 and 12 weeks of age.

Effect of plant age on sesame infection by Alternaria leaf spot

Effect of plant age on sesame infection by Alternaria leaf spot