Cucurbits Physiological disorders. Cucurbitaceae

Physiological disorders of cucurbits.

1. Physiological disorders of cucurbits Kavya D.O. 1 st Year PhD (Horticulture) Department of Vegetable Science, College of Horticulture, Bagalkot. Dept. of VSC 31-08-2023 1

2. Physiological or abiotic disorders are distinguished from other disorders in that they are not caused by living organisms (viruses, bacteria, fungi insects etc), but are caused by non- living, abiotic situations and cause a deviation from normal growth. They are physical or chemical changes in a plant from what is normal and generally caused by and external factor. Most of the physiological disorders are not reversible once they have occurred. Physiological disorders have a major role in hammering the yield and quality of fresh vegetables. Dept. of VSC 31-08-2023 2

3. 1. Nutritional physiological disorders – Eg. blossom end rot in water melon and tomato. 2. Temperature physiological disorders (low and high) Eg. sunburn on the shoulders of tomato,(high-temperature injury occurred prior to harvest). 3. Respiratory physiological disorders - low oxygen and or high carbon dioxide concentrations in and/or around harvested produce in CAS and MAP. Eg. black heart of potato (low-oxygen injury). 4. Miscellaneous disorders- which are product-specific in terms of symptoms expressed. Eg. a) Bitterness (isocoumarin accumulation) in carrot. b) Greening of potatoes exposed to light Physiological disorders can be divided into four general categories : Dept. of VSC 31-08-2023 3

4. Preharvest environment conditions Temperature Nutrition Water regimes Crop development factors (e.g. yield or crop load, position on the plant and carbohydrate, water and /or nutrient partitioning) Postharvest environment conditions Temperature regime Gas atmosphere Storage time 4 Causes of physiological disorders Dept. of VSC 31-08-2023 4

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6. Cucumber Dept. of VSC 31-08-2023 6

7. Disorder Cause Symptoms Remedy Crooked fruit or crooking Imperfect Pollination and fertilization Curved fruit Optimum irrigation and nutrition scheduling may prove to be helpful. Pillow Ca deficiency Abnormal white styofoam like porous textured tissue is formed in the mesocarp of the fruits Apply calcium adequately Fruit splitting or cracking Heavy rainfall or rain after long period of water stress The cracking is mostly vertical initiated from the basal part of the fruit. Improving moisture conservation in soil will help reduce cracking. Dept. of VSC 31-08-2023 7

8. Water Stress and Storage Environment Affect Pillowy Fruit Disorder in Cucumber Pillowy fruit disorder (PFD) was more frequent (110% to 150%) and more severe (59% to 81%) in freshly harvested fruits from stress plots when compared to controls. No after-storage differences in PFD were detectable between water stress treatments. Mean PFD ratings of processed fruit following postharvest storage at 26.5C and either 60% or 75% relative humidity were significantly higher than ratings of fruit stored at either 10.5 or 15.5C and 85% relative humidity. The progressive development of pillowy and the observed enhancement of PFD symptoms following storage at higher storage temperatures indicated that postharvest changes can occur in fruit mesocarp tissue and that the development of PFD can be altered, to some extent, during storage. Negative correlations (– 0.18 to – 0.78) between fruit quality and PFD ratings suggested that these changes can affect processed product quality. Thomas et al .,1992 Dept. of VSC 31-08-2023 8

9. Disorder Cause Symptoms Remedy Light belly colour Direct contract of the fruits with moisture, soil suppresses development of normal fruit colour. The side of the fruit touching moist, cool soil turns to yellow or whitish yellow. Use of plastic mulch can check contact of fruit with moisture soil helping to avoid this disorder. Misshapen fruits Environmental factor adversely affecting pollination and Fertilization. This refers to formation of abnormal- shaped fruits with reduced market value. Keep the optimum plant population. Maintain uniform soil moisture throughout the crop period. Dept. of VSC 31-08-2023 9

10. Squashes Dept. of VSC 31-08-2023 10

11. It is a physiological disorder of summer squash ( cucurbita pepo ) This disorder occurs due to moisture scarcity The leaves beco m e si l v er c o loured and contain less chlorophyll P hotosynthesis i s ha m pered i n t h e silvered leaves Control : Apply a d equ a te a n d freque n t irrigation LEAF SILVERING Dept. of VSC 31-08-2023 11

12. Unfruitfulness in pointed gourd: Pointed gourd is a dioecious cucurbit. So, male and female plants are separate. A common problem is met where pistillate flowers in female plants are shed due to lack of pollination and fertilization. In some cases, ovary of the unfertilized flower may flow a bit due to parathenocarpic stimulation which also abscise after a few days. Control: Male plants must be grown in the field along with the female plants at the rates of 10-12 male plants per 100 female plants to ensure adequate pollination and fruit set. Hand pollination may be done successfully to achieve fruit set. Hand pollination to the female flowers should be done in the early morning hours because stigma receptivity decreases with an advancement of the day. Dept. of VSC 31-08-2023 12

13. Watermelon Dept. of VSC 31-08-2023 13

14. Symptoms: The blossom end of the fruit develops a dark leathery appearance. Symptoms may progress until the entire end of the fruit turns black and rots Cause: This disorder is associated with insufficient calcium uptake and alternating periods of wet and dry soil Damage to the root system may also account for decreased calcium uptake and the development of blossom-end rot Control: Minimized by mulching to maintain constant soil moisture, applying calcium fertilizers and avoiding high levels of nitrogen. Drip irrigate crop to control water management BLOSSOM-END ROOT Dept. of VSC 31-08-2023 14

15. Blossom-end rot of watermelon in the southern region of Oman Dept. of VSC 31-08-2023 15 Blossom-end rot, a non-parasitic disease, was found to occur widely on some oblong varieties of watermelon, causing much damage in the southern region of Oman (Dhofar). Fruit contact with soil surface seems to be the major agent of blossom-end rot of watermelon, especially in the early stage. Incidence of watermelon blossom-end rot was apparently reduced by mulch using a mixture of dried grasses or coconut leaves. Hammouda et al ., 1987

16. HOLLOW HEART Symptoms: Cracks in internal watermelon fruit flesh can occur due to accelerated growth in response to ideal growing conditions. Cause: There is a genetic component to this disorder, but growing conditions can account for much of the variation observed. It appears to be associated with conditions that result in poor pollination followed by rapid fruit growing conditions. Control: Avoid watermelon varieties with a tendency to exhibit hollow heart. Implement best practices for irrigation and fertilization programs. Dept. of VSC 31-08-2023 16

17. Dept. of VSC 31-08-2023 17 Maynard et al ., 1999 Watermelon Fruit Disorders

18. Symptoms: Papery white areas develop on fruit Cause: Develops during hot summer weather when fruit are suddenly exposed to direct sunlight Control: Minimized by maintaining strong vine growth to ensure the fruit is covered SUNSCALD Dept. of VSC 31-08-2023 18

19. Delay in fruit ripening This problem is particularly important in muskmelon and watermelon. Delay in repining is sometime associated with less sweetness and cracking of fruits which occur due to high moisture level and temperature fluctuation at ripening stage Control: Irrigation should be stopped at the ripening stage to hasten ripening Sowing time should be adjusted in such a way that fruits ripe in hot and rainless condition which hastens ripening and at the same time improve sweetness of the fruits Dept. of VSC 31-08-2023 19

20. 31-08-2023 Dept. of VSC 20 Fruit disorders Leaf / plant disorders of cucurbits Poor pollination Bitterness Frost or Low Temperature Injury Drought stress Yellowed foliage due to flooding. Magnesium deficiency Manganese toxicity Molybdenum deficiency Nitrogen deficiency Stem splitting General disorders of cucurbits

21. With the exception of parthenocarpic cucumbers, cucurbits require pollination to produce fruit. Several visits from pollinators on the day that a flower is open are often required to ensure appropriate fruit development. Many fruits will appear misshapen and small when pollination is poor. Fruits will be reduced in size at the stem end . Very high and low temperatures can also affect pollen viability, resulting in poor pollination . If too much nitrogen is used (resulting in excessive vegetative growth) or plants were improperly spaced, bees may have difficulty locating the flowers. Management: Provide pollinators to ensure good fruit set and high yields. Do not spray insecticides during morning hours when flowers are open and insects are actively pollinating plants. 31-08-2023 Dept. of VSC 21 Poor pollination

22. Drought stress Cucurbits are particularly sensitive to drought . Fruit are typically 85% to 90% water and can suffer under drought conditions. Pumpkins often produce long vines with many leaves and can transpire large quantities of water during hot summer days. Severe drought stress affects fruit development, resulting in unmarketable produce. Affected fruit may appear curled, distorted, or tapered at the blossom end; pumpkins become soft and wrinkled.  Management: Irrigate when necessary. 31-08-2023 Dept. of VSC 22

23. Bitterness All cucurbits produce a group of chemicals called cucurbitacins, which cause the vegetables to taste bitter, and the higher the concentration of cucurbitacin the more bitter the vegetable will taste. Mild bitterness is fairly common in cucumbers resulting from higher levels of cucurbitacin triggered by environmental stress, like high temperatures, wide temperature swings or too little water. Uneven watering practices (too wet followed by too dry), low soil fertility and low soil pH are also possible stress factors. Over mature or improperly stored cucurbits may also develop a mild bitterness. 31-08-2023 Dept. of VSC 23

24. Frost or Low Temperature Injury Air temperatures at or slightly below freezing (depending on the extent of radiational cooling) can severely damage all cucurbits seedling stages may be severely stunted or killed by low, but non freezing temperatures because they are "chilling sensitive crops. Damage progresses from a water-soaked appearance of affected leaf tissue or fruit surface immediately after exposure, to a grayish-green scorched" appearance of leaves. Overhead irrigation applied during the low temperature exposure may provide partial protection against a light frost 31-08-2023 Dept. of VSC 24

25. 31-08-2023 Dept. of VSC 25 Yellowed foliage due to flooding. Leaf / plant disorders of cucurbits Magnesium deficiency on muskmelon leaves. Manganese toxicity on a muskmelon leaf.

26. 31-08-2023 Dept. of VSC 26 Molybdenum deficiency of cucurbit crops. Nitrogen deficiency on pumpkins. Stem splitting on watermelon transplants.

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