observation on growth rate of potato plant
Answers
Answer:
All plants vary in their water requirements according to their size and growth stage as well as the length of their maturity and time of year of maximum growth. Possibly no other major crop varies in its sensitivity to water stress based on growth stage than potato. In this section, irrigation recommendations at key production periods are based on the S-shaped growth curves of roots, vines and tubers (Pavlista, 1995) (Table 3). Soil moisture requirements are related to different growth stages (van Loon, 1981). Quality effects of water deficit and excess during these stages are described (Figure 2) (Curwen, 1994 and personal communication). Table 4 summarizes the effects of low and high soil moisture during tuber bulking and maturation stages.
1. Pre-planting to Planting:
A pre-plant irrigation is often recommended for two reasons. First, soil moisture should be about 70-80% field capacity. This will bear-saturate the field, allowing some room for rains. This level amounts to around a quarter of the allowable deficit (AD) of the soil. Soil moisture should be acceptable to support the developing roots after planting and reach emergence. Another benefit from a “pre-irrigation” is the breaking down of clods and clumps for better planting.
2. Planting to Pre-emergence (Sprouting):
[early Stage I. Vegetative (van Loon, 1981)]
Soil moisture in the top foot of soil should be 65 to 80% FC. No irrigation is recommended during this production period. First, seed-pieces at a recommended size, 2 to 2.5 ounces, have sufficient water to support the sprout until emergence. Irrigating during this period would raise the soil moisture and lower soil aeration to a level that would support several pathogens, most notable bacterial soft rot or black leg (Erwinia carotovora), and stem and stolon canker (Rhizoctonia solani). Excess moisture will also decrease tuber respiration, putting the seed-piece under metabolic stress.
3. Emergence to Tuber Initiation (early vine growth):
[Stage I. Vegetative]
This is the log phase of vine growth. Roots are in the second half of their growth. During this period, the vine grows very rapidly, as much as doubling the canopy every week. With rapidly increasing foliage every week, irrigation starts low, 0.5 inch, and gradually increases every week by about 0.5 inches. At tuber initiation, about three weeks after emergence depending on variety, seed health, weather, soil, and cultural practices used, about 1.5 inches of irrigation is applied.
4. Tuber Initiation to Full Bloom:
[late Stage I. Vegetative or Stage II. Tuberization]
In determinate varieties full bloom marks the end of vine growth, while in indeterminate varieties full bloom starts a noticeable slow-down of vine growth, some branching still occurs. The first set of tubers are being initiated and these are in a slow-growth, development stage, the lag phase of tuber growth. Irrigation becomes increasingly important and water stress becomes less tolerable.
5. Full Bloom to Plant Senescence (Tuber Bulking):
[Stage III. Tuber Growth]
At this period, the canopy and roots are fully grown except for indeterminate varieties, which have considerably slowed growth. However, now, tubers are growing rapidly and are in their log phase of growth. Here, it is key to keep in mind that tubers are 76 to 82% water and this water must come from the outside, rain or irrigation. This period runs about six weeks, usually in July and August. Irrigation plus rain should be 2 to 2.5 inches per week or about 15 inches for the period. Soil moisture should be at 80 to 90% FC. This is the period when plants have their highest demand for water and are the most sensitive to a deficit.
6. Plant Senescence to Harvest:
[Stage IV. Maturity]
This period is characterized by dying of the vine; in the case of indeterminate, lower leaves are dying. Tuber growth slows and is in the flat stage. Tuber maturation is a common term used here as tubers settle to their maximum content of dry matter and minimum content of reducing sugars, glucose and sucrose. As the vine dies, tuber skin sets, hardens and adheres to the tuber core (flesh meat etc.). Irrigation declines over this two to five week period depending on variety and climate.
Answer:
Explanation:
E
VER since the fungus Phytophthora infestans first hecame the
subject of scientific investigation, there has been a good deal
of obscurity as to the way in winch it is carried over from year to
year. The conijia are short-lived and therefore do not serve to
tide" the fungus over the winter.
In spite of prolonged search, de Bary' failed to find resting
oospores in diseased potato plants, the fungus in this respect iieing
unlike many other species of Phytophthora. He was of the opinion,
therefore, that potato blight was carried over from year to year by
means of mycelium hibernating in partly diseased tubers, and he
obtained definite evidence tbat mycelium of this kind sometimes
pas8ed from the tubers into young shoots, on which the fungus
developed its spores above ground, thus forming starting points for
an epidemic.
In 1875, Worthington Smith^ reported the discovery of
resting oospores of the blight fungus in tissues of diseased potatp
plants, but the evidence was not conclusive and, in tiie absence of
confirmation by other observers, there has always been doubt whether
these bodies really belonged to Phytophthora infestans.
With the discovery in America by Jones' and Clinton' that
Phytophthora infestans developed oospores in pure culture, attention
was again directed to the possibility of infection arising from such
resting bodies auring the early summer, and Pethybridge' followed
up this line of enquiry in Ireland, Although he confirmed the
development of oospores in culture, he failed to find them in diseased plants. In connection with this work, Pethybridge put to the
test tbe view that the fungus is carried over the winter by mycelium in partly diseased tubers, and, obtained some experimental
evidence that, when planted in pots chiefly under greenhouse
conditions, a very small percentage of blighted tubers functioned in
this way, the great majority either giving rise to perfectly healthy
'
tubers or decaying completely in the soil. Under field conditions
however, none ofthe blighted tubers planted experimentally by him
were seen to throw up shoots invaded by mycelium of Phytophthora
in/estuns derived from the seed sets. In the light of these investi^atioi the blight problem has also been discussed by Home.'
Meiiiu»' in America obtained a considerable amount of evidence
in favour of the view that primary infection arises from mycelium
which hibernates in the seed tubers. Thus a number of partly
diseased tubers planted experimentally in the open threw up one
or more shoots which were Infected by Phytophthora and served as
starting points for an epidemic.
In connection with the perennation of potato blight by means
of mycelium in diseased tubers, mention may be made of the
possibility of shoots becoming infected while the tubers are stored
in clamps or after being discarded from these and left lying near
them. Such shoots may give rise to spores in the late spring or
early summer under favourable weather conditions, and these may
6erve to infect growing crops close at hand, although there is no
publishedevidenceof the occurrence of an outbreakarising in this way.
Portions of blighted tubers left in the soil from the pi'evious
crops or introduced with the manure (e.g., from pigs) may also, perhaps give rise to conidia of Phytophthora when lying near the surface
of the soil, but such diseased tissues usuallybecomeinvaded by secondary organisms which cause complete'disintegration.
Theii are of course other ways in which the blight fungus
might hibernate. Its mycelium may perhaps live saprophytically
in the soil but this is unlikely for Phytophthora infestans is by no
means an easy fungus to grow artificially and in competition with
other oi'ganisms would probably soon collapse. The intervention
of an alternate host has sometimes been invoked but there is no
evidence that such exists, and other plants e.g., tomatoes, which
occasionally become infected by Phytophthora infestans in this
country, are only attacked after an epidemic has begun in potatoes.
Horneshoulddo thesamein the Isle of Wight, butafter making some
preliminary visits to the island, the latter was unfortunatly prevented by illness from continuing the work, the direction of which
then devolved upon Professor P. W. Oliver and the writer.
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