The environmental and physiological causes of cracking or splitting of soft fruits and citrus as they ripen are not well understood. This paper explores factors contributing to radial cracking in tomatoes, gives suggestions for prevention of cracking, and suggests directions for future research. Fruit cracking occurs when there is a rapid net influx of water and solutes into the fruit at the same time that ripening or other factors reduce the strength and elasticity of the tomato skin. In the field, high soil moisture tensions suddenly lowered by irrigation or rains are the most frequent cause of fruit cracking. Low soil moisture tensions reduce the tensile strength of the skin and increase root pressure. In addition, during rain or overhead irrigation, water penetrates into the fruit through minute cracks or through the corky tissue around the stem scar. Increases in fruit temperature raise gas and hydrostatic pressures of the pulp on the skin, resulting in immediate cracking in ripe fruit or delayed cracking in green fruit. The delayed cracking occurs later in the ripening process when minute cracks expand to become visible. High light intensity may have a role in increasing cracking apart from its association with high temperatures. Under high light conditions, fruit soluble solids and fruit growth rates are higher. Both of these factors are sometimes associated with increased cracking. Anatomical characteristics of crack-susceptible cultivars are: 1) large fruit size, 2) low skin tensile strength and/or low skin extensibility at the turning to the pink stage of ripeness, 3) thin skin, 4) thin pericarp, 5) shallow cutin penetration, 6) few fruits per plant, and 7) fruit not shaded by foliage. Following cultural practices that result in uniform and relatively slow fruit growth offers some protection against fruit cracking. These practices include maintenance of constant soil moisture and good Ca nutrition, along with keeping irrigation on the low side. Cultural practices that reduce diurnal fruit temperature changes also may reduce cracking. In the field, these practices include maintaining vegetative cover. Greenhouse growers should maintain minimal day/night temperature differences and increase temperatures gradually from nighttime to daytime levels. For both field and greenhouse tomato growers, harvesting before the pink stage of ripeness and selection of crack-resistant cultivars probably offers the best protection against cracking. Areas for future research include developing environmental models to predict cracking and exploring the use of Ca and gibberellic acid (GA) sprays to prevent cracking.
Mary M. Peet
It is often difficult to obtain information on producing vegetables using `sustainable' practices such as reduced inputs of pesticide and commercial fertilizers. Lack of such information is often cited by conventional farmers and extension agents as a reason for not adopting or assisting others in adopting sustainable techniques. As part of a Southern Region Low Input Sustainable Agricultural (LISA) Program, we are compiling a database which will include techniques for vegetable production acceptable to `organic' farmers as well as those acceptable to conventional farmers. This information source will include information on 17 specific vegetables and well as chapters on general topics such as cover crops and weed control. We hope to make this information available both as a production manual and by way of an electronic information retrieval system. Steps in the development of this project include initially soliciting input from farmers and extension workers on the preferred content and format and conducting an on-going evaluation by these groups as segments are developed. The database should be available within 2 years in both electronic and hardcopy versions.
Mary M. Peet
“Sustainable Practices for Vegetable Production in the South,” 174 pages long, including 250 references, was written as a traditional college textbook. I will be discussing my experiences converting it to a web document and simultaneously releasing web and print versions. I will also discuss some of the issues we will confront if we depend on the web for delivering and receiving information. These issues are: 1)There are no conventions for websites comparable to those that have evolved for print documents. At the same time, users expect sites to function certain ways. 2) Consistency between parts of the website is more difficult to maintain than in a print document, but is critical in order to correctly orient the user. 3) The optimal size and structure of the information “chunk” or subdivision is unclear—Should it be a whole chapter or article, a single paragraph, or a functional unit of facts that does not have a name or correspond to anything in print media? 4) How do you let a person accessing any one part of your website know about all the other parts and how they fit together—You can flip through a book to view it, but a person following a link to a page on your site is like the blind person touching the elephant's trunk—they can not visualize the whole. 5) There is no one intuitively obvious or logical place to put references and footnotes because of the subdivision of information into “chunks” or functional facts. 7) There is no obvious starting or stopping point in making revisions. 8) People accessing the site will send messages and ask questions. 9) Meaningful evaluation of usage and usefulness is difficult.
Mary M. Peet
ASHS 2008 Presidential Address: Mary M. Peet
Mary M. Peet
Mary M. Peet
Sustainable Practices for Vegetable Production in the South, 174 pages long and with 250 references, was written as a traditional college textbook, but is also available as a World Wide Web (Web) site (http://www2.ncsu.edu/sustainable/). This article chronicles the conversion of the entire text to a Web document and the simultaneous release of Web and print versions. I will also discuss some of the issues that we will confront if we depend on the Web for delivering and receiving content-rich information. These issues are as follows. 1) Although there are no standards for Web sites as there are for print documents, there are certain similarities in the way most Web sites function. Relative to our familiarity with book and journal conventions, those of us educated in the age of print are unaware of Web standards. 2) The optimal size and structure of the information chunk is unclear. Should it be a whole chapter or article, a single paragraph, or a functional unit of facts that doesn't have a name or correspond to anything in print media? 3) Organization and consistency are critical. Table and chapter numbers are meaningless. The most important question is “How does a person accessing part of your Web site know about all the other parts and how they fit together?” You can flip through a book to view it, but a person following a link to a particular page on your site is like the blind man touching the elephant's trunk—the whole is hard to visualize. 4) There is no good place to put references and footnotes because of the subdivision of information into chunks of functional facts. 5) There is no obvious starting or stopping point in making revisions. 6) People accessing the site will send messages and ask questions.
M.M. Peet and S. Sato
The effects of chronic, mild heat stress on fruit set, fruit production, release of pollen grains, photosynthesis, night respiration, and anther dehiscence were ex-amined in tomatoes (Lycopersicon esculentum Mill.) differing in high temperature sensitivity. Plants were grown under three temperature regimes: 1) 28/22 or 26/22 °C (optimal temperature) 2) 32/26 °C (high temperature), and 3) 32/26 °C day/night temperatures relieved at 28/22 °C for 10 days before anthesis, then returned to 32/26 °C (relieving treatment). `FLA 7156' was the only cultivar with fruit set at 32/26 °C. All five cultivars, however, had fruit set in the relieving treatment (RT). The longer the relief, the higher was the percentage of fruit set. Longer periods of relief also increased the number of pollen grains released and linear regression analysis showed a significant relationship between the number of pollen grains released and the percentage of fruit set. Germination of pollen grains was also lowered in high-temperature-grown plants. The number of pollen grains produced, photosynthesis, and night respiration did not limit fruit set under chronic, mild heat stress, however. This suggested that cultivar differences in ability to release pollen and to produce viable pollen under heat stress are the most important factors determining their ability to set fruit.
Mary M. Peet and Suguru Sato
Global temperature increases are predicted over the next several decades. Earth surface temperatures in 1995 were the highest ever recorded. At day temperatures above 30C or night temperatures above 21C, tomato fruit production decreases. However, the temperature dependence of fruit production has not been described in terms of whether day temperatures, night temperatures, or mean temperatures are the most limiting. The process or tissue most sensitive to heat and most limiting to fruit production is also not known. The objectives of this experiment are to establish the temperature dependence of fruit set in tomatoes and to determine the importance of post-pollen production effects. We imposed a total of nine temperature treatments in a series of four separate experiments. Each experiment consisted of a 30/24C treatment and two other day/night temperature combinations with differing means and/or day/night temperature differentials. As mean daily temperature increased from 25 to 29C, fruit set, fruit number, total fruit weight, and seediness index (a quantitative rate of fruit seed content) declined. Temperature treatments did not affect average fruit weight. Higher mean temperatures promoted flowering except at the highest temperature. Mean temperature was more important than day/night temperature differentials or the specific daytime or nighttime temperature treatment.
Mary M. Peet and Michael Bartholemew
Lycopersicon esculentum Mill. `Laura' plants were grown in the North Carolina State Univ. phytotron at 26C day temperature and 18, 22, 24, or 26C night temperatures to determine the effects of night temperature on pollen characteristics, growth, fruit set, and early fruit growth. Total and percentage normal pollen grains were higher in plants grown at night temperatures of 18 and 22C than at 24 and 26C, but germination was highest in pollen produced at 26C. Seed content was rated higher on the plants grown at 18C night temperatures than in any of the other treatments. Numbers of flowers and fruit on the first cluster were lower in the 26C night treatment than in the other night temperature treatments. Plant height was greatest but total shoot dry mass was lowest in the 22C night temperature treatments. Fruit fresh mass increased with night temperature, reflecting more rapid development, but the experiment was not continued to fruit maturity, so the effect of night temperature on final fruit size and total plant production could not be determined. Night temperatures of 26C reduced fruit number and percentage fruit set only slightly at a day temperature of 26C, even though these temperatures were above optimal for pollen production and seed formation. To separate temperature effects on pollen from direct or developmental effects on female reproductive structures, pollen was collected from plants in the four night temperature treatments and applied to stigmas of a male-sterile cultivar kept at 24-18C minimum temperatures in adjacent greenhouses. In the greenhouse-grown male sterile plants, no consistent effects of night temperature treatment given the pollen could be seen in fruit set, fruit mass, seed content (either on a rating or seed count basis), seedling germination, or seedling dry mass.
Michael Bartholomew and Mary M. Peet
Previous greenhouse studies in Raleigh have shown that nighttime cooling increases tomato fruit weights from 11% to 53%, depending on planting dates. The physiological mechanism was unclear, except that temperatures during fruitset were most critical We report here on a phytotron experiment comparing pollen characteristics and in vitro pollen germination of plants grown at night temperatures of 18, 22,24 or 26°C in a 12-hour photoperiod with 26°C day temperature in all treatments. There was considerable variability between sampling dates in pollen characteristics and % germination. The most consistent and significant effects were a decrease in total pollen and an increase in % abnormal pollen at high night temperatures. Number of seed present in the fruit also decreased with increasing night temperatures, indicating that the changes in pollen characteristics adversely affected seedset. Night temperatures of 22C appeared optimal for many of the pollen and growth characteristics measured, but fruit developed most rapidly at the higher night temperatures.