Dr' Bennett copy

1
CHAPTER 8 GROWTH AND DEVELOPMENT
Growth is a function of 1) Genotype 2) Envi
ronment Often the environment and genotype
interact strongly to influence plant growth
Some traits are affected primarily by
genotype (i.e., no. of leaves of maize), while
others are primarily affected by environment
(i.e., leaf photosynthetic rate) In modern
crop production, both genotypic and environmental
manipulation are used to maximize crop
productivity
2

• DEFINITIONS
• 1) Microclimate - the environment near the plant
• Growth - (cell division, cell expansion,
• and cell differentiation)
• In a more general sense, plant scientists
  often refer to growth as an increase in dry
  matter

2a) Cell division increase in cell number 2b)
Cell enlargement increase in cell size 2c)
Cell differentiation development of
cells into specialized structures (i.e.,
roots, leaves, flowers, seeds, etc)
3
Fig. 8.1. Growth and differentiation regions
and representative cell types of a maize root
tip. (From Baldovinos 1953)
4
GROWTH FACTORS
I. External Factors (Environmental) a)
climatic (light, temp, water) b) edaphic
(soil texture, pH, CEC) c) biological
(weeds, insects, diseases etc.) II. Internal
Factors (Genetic) a) stress resistance
b) PS rate c) RS rate d)
partitioning e) enzyme activities
f) type and location of meristems g)
many others
5
Fig. 8.2. Some of the limiting factors in crop
production. (Courtesy of American Potash
Institute)
6
Law of the Minimum The growth factor in lowest
supply sets the capacity for yield.
Fig. 8.3. Law of the minimum, illustrated by a
barrel with staves of different heights.
Nitrogen, the lowest stave, establishes the
maximum capacity of the barrel and, by analogy,
the maximum possible growth.
1st Proposed by Liebig in 1862.
7
Blackmans Theory of Optima and Limiting
Factors
Blackmans theory of optima and limiting
factors states that when a process is
conditioned as to its rapidity by a number of
separate factors, the rate of the process is
limited by the pace of the slowest factor.
8
PS
Radiation
9
The response observed is dependent on
how deficient the input is to begin with, i.e.,
larger response if input is severely limiting.
10
Mitscherlichs Law of Diminishing Return
Mitscherlich Law of Diminishing Return (1909)
- curvilinear response, that is plant growth
increases with additional increments of a
limiting factor, but not in direct
proportion. 1) The above descriptions of
limiting factor responses are theories and not
laws 2) They make a convenient way to look at
limiting factors, but in actuality more than one
factor is often simultaneously limiting.
11
dy C (A-Y) dx
dy change in crop yield dx change in
limiting factor (growth factor) C constant
(dependent on growth factors) A maximum
possible yield Y actual yield at any level of
X From this equation, as (A-Y) decreases
(actual yield becomes more), dy/dx decreases.
Less return for addition of limiting factor is
achieved as Y approaches A.
12
MERISTEMS
13
Types of Meristems
a) Apical - (at the tip) - this increases length
or height. Gives growth at tip of shoot or
root increases height or length. b)
Lateral - (causing branching or increasing dia-
meter) . They expand the breadth and diameter
of an organ. - cambium (secondary
xylem and phloem) - in expanding leaves (at
margins) c) Intercalary (between
differentiated tissues)
14

• Types of meristems
• Lateral
• Apical
• Intercalary

15
GROWTH
Sigmoid curve best characterizes growth over
a generation and demonstrates four phases 1)
Exponential 2) Linear 3) Dampened
exponential 4) Steady state (physiological
maturity) Similar to one-celled organisms,
small plants (with no competition from one
another) will grow exponentially
16
Growth (cont)
As competition among plants occurs, the
growth becomes near-linear, rather than
exponential In crops, exponential phase is
relatively short, and it is the linear
phase of growth that is most important for
total productivity, since it occurs over a long
time period during the growth of the crop
Senescence or maturity ends the linear phase of
growth
17
GROWTH ANALYSIS
Growth Analysis Analysis of yield influencing
factors and plant development as net
photosynthate accumu- lation is naturally
integrated over time. Two measurements, leaf
area and dry weight, are measured at
frequent intervals as the crop grows Other
quantities are calculated Advantages
simple LA photoelectric device or
(LxW) x constant Dry weight-balance
18
Growth Analysis - Calculations
Crop Growth Rate increase in dry weight per
unit land area
per unit time Seed Growth Rate increase in
seed dry weight per
unit land area per unit time Partitioning
Coefficient ratio of seed growth rate to
crop growth
rate SGR/CGR Partitioning coefficient
19
(No Transcript)
20
From Fig 8.11
Days 60 120
Total dry wt. 300 1800
Ear dry wt. 250 1250
days 100 140
----g m-2---
CGR
25 g m-2 d-1
Partitioning coefficient