Search Results

You are looking at 11 - 20 of 74 items for

  • Author or Editor: Thomas E. Marler x
Clear All Modify Search
Free access

Thomas E. Marler and Philip W. Marler

The eyecare industry has used various instruments and methods for determining intraocular pressure. Some of the methods may be applicable for measurement of fruit firmness in the horticultural industry. We determined fruit firmness with an applanation tonometer, currently one of the most popular instruments in the eyecare industry. We then measured firmness of the same sample using a penetrometer with an 8-mm probe. Kiwi, mango, peach, strawberry, tomatillo, and tomato fruit were included in the study. With the exception of mango, tonometer and penetrometer measurements within a species were significantly correlated. The contact area of the tonometer probe was 1.5 mm2, which was less than 3% of the contact area of the penetrometer probe. The heterogeneous nature of mango mesocarp due to fibers and this large difference in contact area between the two instruments may have caused the lack of correlation for that species. The data indicate that tonometry may be useful for determining firmness of fruit, and further development may lead to a nondestructive method of obtaining these data.

Free access

Thomas E. Marler and Yasmina Zozor

Leaf gas-exchange responses of A. souamosa seedlings to salinity were studied in sand culture in a series of glasshouse experiments. Trees were irrigated with a complete nutrient solution as the control, or with this solution amended to 3 or 6 dS/m with sea salt. Inhibition of net CO2 assimilation, stomatal conductance of CO2, and transpiration was apparent 14 days after treatments were imposed, and continued to decline until day 30 to 35. The diurnal pattern of leaf gas exchange was not altered by salinity. Salinity reduced CO2, light energy, and water use efficiencies. Dark respiration and internal partial pressure of CO2 were unaffected by salinity stress. Results indicated that substrate salinity inhibited photosynthesis of A. souamosa via limitations on mesophyll capacity for CO2 assimilation and had little effect on gas phase limitations.

Free access

Thomas E. Marler and Olympia Terral

Free access

Thomas E. Marler and Nirmala Dongol

The profile of nonstructural carbohydrates (NSC) was quantified to determine sugar and starch relationships of megagametophyte tissue during Cycas micronesica K.D. Hill seed ontogeny. Field work occurred in northern Guam where megastrobili were marked and dated as they emerged from stem apices of plants in a natural population. Seeds were harvested beginning 6 months after megastrobili emergence and continuing until 28 months, and gametophyte tissue was separated from the remainder of each seed. Carbohydrates within lyophilized gametophyte tissue were quantified by high-pressure liquid chromatography. The levels of glucose and fructose declined from a high at 6 months to a homeostasis at 11 months, and the levels of sucrose similarly declined from 6 months to a homeostasis at ≈14 months. Starch content exceeded sugar content and increased from 6 months to reach a homeostasis at ≈18 months. Maltose was not detected in any sample. Stoichiometric quotients changed dramatically until ≈14 months, when they became fairly stable until 28 months. Starch concentration was ≈5-fold greater than sugar concentration at 6 months, and increased to ≈15-fold greater than sugar concentration by 28 months. Total NSC in mature megagametophytes was almost 70% on a dry weight basis. Our results are in agreement with the biological function of this haploid tissue, as copious carbohydrate resources are readily available to support embryo and seedling growth.

Free access

Thomas E. Marler and Aubrey Moore

The cycad aulacaspis scale (Aulacaspis yasumatsui Takagi) has invaded numerous geographic regions in the past 15 years. The sequential invasions have decimated many Cycas nursery and landscape industries and threatened C. micronesica K.D. Hill and C. taitungensis C.F. Shen, K.D. Hill, C.H. Tsou and C.J. Chen within their native habitats. The majority of the international cycad trade is dominated by Cycas revoluta Thunberg. We removed dense tomentum that characterizes C. revoluta cataphylls and excised intact leaf bases from stems of landscape C. revoluta plants to expose hidden surfaces. Additionally, we removed the root system from containers on nursery plants to reveal enclosed roots. All three organs were infested with cycad aulacaspis scale on tissue surfaces that cannot be detected during thorough visual inspection of intact plants. These unique concealed infestations allow this species to vector scale insects in a cryptic manner on cataphyll, stem, and root surfaces. This information lends support for a policy of strict prohibition of imported C. revoluta plants from countries known to have cycad aulacaspis scale infestations.

Free access

Thomas E. Marler and Nirmala Dongol

We used activated charcoal methods to test for the presence of phytotoxic substances in soils that had received inputs of decomposing Cycas micronesica K.D. Hill leaves and stems that were heavily infested with the armored scale Aulacaspis yasumatsui Takagi. Velocity of Momordica charantia Descourt. and Carica papaya L. seedling emergence was increased by the addition of charcoal to these soils. Furthermore, M. charantia and C. papaya seedling height and dry weight were among the response variables that were increased by the addition of charcoal. Legacy effects of scale-infested C. micronesica plant litter deposited in these soils resulted in phytotoxic compounds that inhibited seedling emergence and plant growth. Scale-infested Cycas leaves should not be used as mulch or in compost until phytotoxic causal mechanisms are more fully understood.

Free access

Thomas E. Marler and Yasmina Zozor

Growth and leaf gas-exchange responses of carambola (Averrhoa carambola L.) seedlings to wind or seismic stress were studied under glasshouse conditions. Forty days of twice daily seismic stress applied for 10 seconds consistently reduced carambola height, leaf area, dry weight, relative growth rate, and leaf-area ratio, but increased trunk cross-sectional area compared with plants receiving no seismic stress. Fifty-one days of wind load reduced plant height, leaf area, dry weight, trunk cross-sectional area, net assimilation rate, relative growth rate, leaf-area ratio, and stomatal conductance compared with plants receiving no wind stress. Morphological appearance was similar for plants receiving wind or seismic stress. Net CO2 assimilation of carambola leaflets was reduced by 30 minutes of wind load for up to 6 hours following the stress. Results suggest that wind may reduce carambola growth at least partially by influencing leaf gas exchange or by the mechanical stress associated with wind.

Free access

Thomas E. Marler and Yasmina Zozor

Whole plant growth, foliage mineral content, and leaf gas exchange were measured on Mammea americana seedlings exposed to salinity ranging from 0 to 8 dS·m–1 to determine relative tolerance of this species. In one study, growth measured as leaf area, trunk cross-sectional area, and total dry mass was reduced by 23 weeks of exposure to salinity. Growth of plants exposed to 8 dS·m–1 was

≈30% below that of control plants. Leaf gas exchange was reduced by salinity to a greater degree than the growth variables. Stomatal conductance of plants exposed to 8 dS·m–1 was ≈70% below that of control plants. Plants exposed to 8 dS·m–1 exhibited a seven-fold increase in leaf chloride and 13-fold increase in leaf sodium compared to the control plants. In a second study, 8 weeks of exposure to 8 dS·m–1 reduced net CO2 assimilation and apparent quantum yield to ≈50% of the values for the control plants. Dark respiration was not influenced by salinity. The results indicate that Mammea americana is moderately sensitive to salinity stress.

Free access

Thomas E. Marler and Cecil Stushnoff

The influence of plant size on recovery following defoliation of `Tainung 1' papaya was used to study the role of respiratory sink size relative to photosynthetic surface area and the carbohydrate pool size available for remobilization. Defoliated (D) plants at three different ages: oldest, 24 weeks posttransplant (PT), supporting ≈8 weeks of fruit set; intermediate, 10 weeks PT, ≈2 weeks from initial flowering; and youngest, 4 weeks PT, were compared to an equal number of control plants. The oldest plants abscised all fruit <5.5 cm in diameter as a result of defoliation. Increase in stem height and basal circumference ceased on all plants and increase in fruit circumference ceased on the oldest plants following defoliation. Increase in stem height of D plants began again 3 weeks postdefoliation (PD) and returned to that of control plants by 6 weeks PD. Increase in basal circumference of D plants began again 6 weeks PD. Root density was observed on observation windows, and fine roots completely disappeared within 1 week PD. Root density returned to that of control plants by 6 weeks for the youngest and intermediate plants and by 8 weeks for the oldest plants. Increase in fruit circumference of pre-existing fruit for the oldest D plants never returned to that for control plants. These plants began setting fruit again ≈8 weeks PD. Defoliation delayed initial flowering of the intermediate plants 6.5 weeks and of the youngest plants ≈2 weeks. Thus, the greatest impact of defoliation on reproductive growth occurred with the two oldest age groups.