Detached Leaf Discs Research Articles

Sensitivity to cymoxanil in populations of Plasmopara viticola in northern Italy

In 1993, control failures were reported on grapevine in northern Italy under severe downy mildew pressure after postinfection application of cymoxanil in mixtures with copper or mancozeb. A monitoring survey was started immediately in Piedmont (north‐western Italy) in order to determine the sensitivity of populations of Plasmopara viticola to cymoxanil from those vineyards where the fungicide was not controlling the disease satisfactorily. In 1994 and 1995, monitoring surveys were extended to north‐eastern Italy, where cymoxanil mixtures were not performing as well as in the past. Sampled populations were tested on detached leaf discs and on whole potted plants under controlled conditions. In 1993, 12 populations, sampled in Piedmont, showed MIC values (minimum inhibitory concentration) varying from 10 to more than 100 mg L−1 cymoxanil. With a baseline reference population having a MIC value of 3 mg L−1, resistance factors ranged from 3 to more than 30. In 1994, 17 populations out of 27 sampled in Trentino (north‐eastern Italy) showed MIC values of 100 mg L−1 or higher and in 1995, 32 populations out of 38 showed the same behaviour. In similar experiments, the MIC values of populations from nontreated plots were between 3 and 10 mg L−1. In whole potted plant tests, populations with MIC values higher than 200 mg L−1 in a leaf disc test were not controlled by 500 mg L−1 of cymoxanil. The results of our study suggest that resistance to cymoxanil in P. viticola may contribute to a lack of disease control in Italian vineyards.

Correlation between the inhibition of photosynthesis and the decrease in area of detached leaf discs or volume/absorbance of protoplasts under osmotic stress in pea (Pisum sativum)

Exposure to osmotic stress reduces leaf area and protoplast volume while decreasing photosynthesis. But the measurement of protoplast volume is tedious, while rapid determinations of leaf area in the field are difficult. We evaluated the quantitative relationship between the extent of decrease in area of detached leaf discs or the volume of protoplast of pea (Pisum sativum) and reduction in their photosynthetic capacity under osmotic stress. Osmotic stress was induced by increasing sorbitol concentration in the surrounding medium of the leaf discs from zero to 1.0 M (‐3.1 MPa), and in case of protoplasts from 0.4 M (‐1.3 MPa, isotonicity) to 1.0 M (‐3.1 MPa, hypertonicity). There was a high degree of positive correlation between the extent of reduction in the area of detached leaf discs or the volume of protoplasts (indicated by diameter or absorption at 440 nm) and the decrease in photosynthesis. The correlation coefficients between inhibition of photosynthesis and the decrease in leaf disc area or protoplast volume were 0.96 and 0.99, respectively. We therefore suggest that the decrease in absorbance at 440 nm (corrected for turbidity at 750 nm) can be used as a simple measure to predict the inhibition due to osmotic stress of photosynthesis in mesophyll protoplasts. Similarly, the reduction in area of detached leaf discs could also be a very simple and useful criterion to assess osmotic tolerance of photosynthesis.

Correlation between the inhibition of photosynthesis and the decrease in area of detached leaf discs or volume/absorbance of protoplasts under osmotic stress in pea (Pisum sativum)

Correlation between the inhibition of photosynthesis and the decrease in area of detached leaf discs or volume/absorbance of protoplasts under osmotic stress in pea (Pisum sativum)

Plant Resistance to Twospotted Spider Mite (Acari: Tetranychidae) in Raspberry Cultivars

Eighteen raspberry ( Rubus idaeus L.) genotypes were evaluated for resistance to the twospotted spider mite, Tetranychus urticae Koch, using detached leaf disk and intact leaf cage tests. Egg production was consistently lower on J9 compared with several of the other cultivars and selections tested. Preliminary evidence suggests that J9’s resistance has a genetic basis. Antixenosis appears to be one possible mechanism of resistance. Boysenberry, R. ursinus Cham & Schlect × Not Known, and kiwifruit, Actinidia deliciosa Liang & Ferguson, were exceedingly poor hosts for the twospotted spider mite.

The evaluation of antibiosis of selected lines for resistance of melon to the carmine spider mite Tetranychus cinnabarinus (Acari: Tetranychidae)

AbstractAntibiosis of resistant melon lines to the carmine spider mite, Tetranychus cinnabarinus (Boisduval), was evaluated in the laboratory. Significant differences among lines were observed seven days after the inoculation of detached leaf disks. The most resistant lines, namely CHI-8, BUS-7 and BUS-3, reduced the average mite daily fecundity by 49%, 40% and 33%, respectively, as compared to the susceptible NY line. Resistance did not appear to be related to the growth habit. Selfing resistant melon parents resulted in a significant increase in the number of plants on which female mites produced less than one egg per day.

Ceratocystis fimbriata, causal agent of basal rot of Syngonium cultivars, and host rang studies of isolates of C. fimbriata in Australia.

Inoculation of plantlets of Syngonium sp. with various combinations of Ceratocystis fimbriata, and Colletotrichum dematium or Stilbella sp. indicated that C. fimbriata is the principal cause of basal rot disease of Syngonium. Of a range of plants tested, Syngonium cultivars, Caladium, Aiocasia, Crotalaria and Xanthosoma spp. were susceptible to damage by C. fimbriata, with Xanthosoma the least susceptible. C. fimbriata also colonised Colocasia esculenta in detached leaf disc tests.

Influence of 2-(3,4 dichlorophenoxy)-triethylamine on photosynthesis of Phaseolus vulgaris L.

The effect of foliar sprays of the growth regulator 2-(3,4 dichlorophenoxy)-triethylamine (DCPTA) on net photosynthesis (Pn) by intact bean plants depended upon concentration and the stage of development of the leaves. A single foliar spray of 2.0 mM DCPTA reduced Pn when applied to young expanding leaves but had little effect on fully expanded leaves. Lower DCPTA concentrations (0.2 to 0.8 mM) had no effect on Pn, unless applied more than once which resulted in reduced Pn. The DCPTA-induced inhibition of Pn was associated with chlorosis and aberrations in chloroplast ultrastructure. DCPTA did not affect stomatal resistance. When applied to detached leaf disks in the dark, DCPTA retarded the normal loss of chlorophyll suggesting that DCPTA may have anti-seneseent properties.

New Technique for Measuring the Water Potential of Detached Leaf Samples

AbstractEvaporative losses and contamination in sample disks after they are cut from plant leaves often cause errors in measurements of water potential. A new technique for collecting detached leaf disks to measure water potential eliminates most of the errors associated with other methods. The leaf cutter contains a double‐junction Peltier thermocouple psychrometer. When a leaf disk is removed from the plant, it can be sealed immediately against the cavity containing the psychrometer.

Characterizing Resistance to Tetranychus urticae in Tomato12

Five tomato lines selected for resistance to the two-spotted spider mite, Tetranychus urticae Koch, were studied to characterize the nature of their resistance. Highly resistant PI 251303, moderately resistant ‘Anahu’ and ‘Kalohi,’ and low-resistant ‘Roma’ and T-526 were tested by 3 different procedures to define the nature of resistance. Detached leaf disks rimmed with tanglefoot were inoculated with teneral female mites and counts Were obtained on mites that died on the leaf, as a measure of antibiosis; mites that were trapped in the tanglefoot, as a measure of repellency; and oviposition, as a measure of food acceptibility and fecundity. High numbers of mites feeding on PI 251303 were either killed or repelled into the tanglefoot, and there was direct acaricidal action attributable to leaf hair exudate. This was velified by topical application of the exudate to mites. Fewer numbers of mites inoculated on leaf disks from the other lines either died or were trapped in the tanglefoot as compared with PI 251303.

Effects of Soil Insecticides and Absorbents on Plant Sugars and Resulting Effect on Mite Nutrition1

The effects of DDT and various absorbent materials as soil additives on the composition of Black Valentine beans and Clark soybeans and on the Tetranychus telarius (L.) populations developing thereon were investigated in the greenhouse. Treatments included DDT only at 800 or 1,600 pounds per acre and DDT at both levels in combination with six levels of the absorbent material as well as an untreated check. Mite development was measured by counting the progeny developing over a period of 8 days from five young adult female mites introduced to a detached leaf disk, each disk being one of four replicates. Dry weight of foliage was calculated and foliage was analyzed for total and reducing sugar, total nitrogen, phosphorus, and potassium. Analyses for correlation coefficient (r) were made on populations with the results of the foliage analyses. In Black Valentine beans DDT added to the soil at both 800 and 1,600 pounds per acre increased total and reducing sugars, nitrogen and T. telarius populations over the untreated check, while decreasing phosphorus, potassium, and dry weight of foliage. Addition of Hydrodarco B, Aqua Nuchar A, and Nuchar C-115-A generally restored the chemical components of the beans and also the mite populations to the levels of the untreated check. Mite populations were thus correlated positively with reducing sugar and nitrogen, in some cases total sugar, and negatively with per cent phosphorus, potassium, and dry weight of foliage. Peat moss, calcium hydroxide, and Fisher activated charcoal pellets did not function effectively as absorbents; Norit-A and Mallinckrodt activated charcoal alleviated the phytotoxic effects of DDT but did not influence mite populations consistently. Clark soybeans were not as sensitive to DDT as Black Valentine beans. The percentages of reducing and total sugar were elevated much less and lower concentrations of absorbent were required to reduce these values to the original levels. Hydrodarco B was the only absorbent to affect the chemical composition and mite populations as consistently as in Black Valentine beans although similar trends were noted with Aqua Nuchar A and Nuchar C-115-A. These studies demonstrated that at least one organic constituent of the plant, reducing sugar, has been markedly influenced in the plant by the addition of high levels of DDT to the soil. Also it has been shown that these plant sugars can be related to the development of a plant feeding mite such as T. telarius.