Physiologically Induced Heat Stress Posing Problems in Seed

Physiologically Induced Heat Stress Posing Problems in Seed

Physiologically Induced Heat Stress Posing Problems in Seed Potatoes.
Willie Kirk, Pavani Tumbalam, Ray Hammerschmidt and Phillip Wharton. Plant Pathology.
A heat-induced problem affecting seed tubers produced in MI during 2007 may have manifested itself in
reduced seed quality for 2008. Tests conducted at MSU have shown that seed tubers are failing to
completely suberize after cutting (Fig. 1). This has been seen mainly in the variety Snowden although may
be present in other varieties. Tubers that have been cut lose water rapidly from the cut surface and fail to
suberize and internal sections become translucent. Over a period of about 24-hours the tubers oxidized
but did not form a protective layer of suberin. We tested starch content using a potassium iodide test and
it was clear that the non-suberizing tubers had less starch than tubers (Snowden) taken from a storage
sample from MSU (Fig. 2). We hypothesize that the seed tubers were heat-stressed last season during
the very hot late summer and early fall. Temperatures in the areas where these tubers came from are
summarized in Table 1. Although average soil temperature at 2 and 4” depths was not extreme there
were several days during the tuber development period when soil temperature was in excess of 80°F. We
speculate that under these conditions tubers physiologically aged more rapidly than normal. As a result
starch breakdown especially in the oldest cells at the center of the tubers was accelerated, resulting in
cells without sufficient energy for normal processes, such as suberization after cutting.
Of special note is the damage to tubers after a three-way cut. The tuber flesh under the cut is necrotic
(Fig. 3). This means that the cells are dead and therefore unable to actively suberize after cutting. These
symptoms are very similar to the necrosis seen in virus-affected tubers and we are checking that
possibility over the next week but we think that this is a necrosis more normally associated with heatinduced stress.
These tubers are therefore more prone to infection by secondary pathogens, especially soil-borne
pathogens after planting. The following recommendations are set out to help growers manage seed from
all sources in MI for 2008.
Cutting and re-storage operations.
• Do not make more than a single cut to seed – splitters have had less tuber necrosis than 3 or 4way cut seed and tend to suberize better.
• At cutting, apply a seed treatment such as Maxim MZ, Moncoat MZ or Tops MZ, or a bark-based
seed treatment to enhance healing and protect against seed and soil-borne pathogens. Do not
reduce the rates.
• If delayed in planting, place tubers in piles over vents to a maximum height of 8-ft.
• Force air through the pile to enhance aerobic wound-healing.
• Slowly increase temperature of the pile to enhance sprout development at about 1°F /day up to a
maximum of 55°F.
• MSU does not recommend hydrogen dioxide (e.g. Oxidate) as a seed treatment.
Planting
• Where possible wait until the soil is at the same temperature or 1 – 2°F warmer than the seed (5557°F).
• Plant seed at a maximum of 4” depth to the upper surface of the tuber.
• At 75% emergence, hill the crop to attain your desired hill height or wait until you are sure that all
delayed sprouts have emerged.
• Do not re-cultivate; attempt to reduce stress to the plant wherever possible.
In-season management (seed crops)
• Although soil temperature conditions cannot be predicted the temperature of the environment
should be managed where possible with irrigation.
• The ideal soil temperature to avoid heat stress or heat induced physiological aging is about 65°F.
Figure 1. Cut seed tubers (cv. Snowden) showing cell death in heat stressed tuber to the left of each pair
compared to a tuber taken from MSU storage. The stressed tubers did not suberize and pits formed in the
tuber flesh along with necrotic areas.
Figure 2. Starch content using a potassium iodide test. The more intense purple color indicates higher
starch content. The non-suberizing tubers had less starch than tubers (Snowden) taken from a storage
sample from MSU.
Figure 3. Necrosis at the junction of a tuber after a three-way cut. The tuber was cut about 7-days prior
and the tuber flesh under the cut is necrotic. This means that the cells are dead and unable therefore
unable to actively suberize after cutting .
Table 1. Meteorological parameters for Elk Rapids (NW Michigan LP) from Jul 1 to Sep 30, 2007.
Date
7/1/07
7/2/07
7/3/07
7/4/07
7/5/07
7/6/07
7/7/07
7/8/07
7/9/07
7/10/07
7/11/07
7/12/07
7/13/07
7/14/07
7/15/07
7/16/07
7/17/07
7/18/07
7/19/07
7/20/07
7/21/07
7/22/07
7/23/07
7/24/07
7/25/07
7/26/07
7/27/07
7/28/07
7/29/07
7/30/07
7/31/07
8/1/07
8/2/07
8/3/07
8/4/07
8/5/07
8/6/07
8/7/07
8/8/07
8/9/07
8/10/07
8/11/07
8/12/07
8/13/07
8/14/07
8/15/07
8/16/07
8/17/07
8/18/07
8/19/07
Air temperature (F)
Maximum
Minimum
70.2
39.1
75.3
45.1
81.4
54.3
81.8
57.7
82.1
55.1
80.4
51.2
88
53.7
94.4
70.5
84.1
61.7
86.6
59.6
72.6
57.3
72.2
53.9
71.7
55
69.8
54.3
75.5
51.3
79.1
46.8
84.2
47
84.8
51.8
71.5
56.8
69.8
46.5
77.2
40.4
83
44.8
85
49.9
86.1
54.7
91.4
57.5
84.4
63.1
82
66.7
85
55
87.6
50.3
92.5
55.5
95.5
59.9
94.4
59.3
89.9
71.3
82.2
53.8
84.8
43.9
84.5
57
86.1
63
91.1
59.3
80.2
55.5
85.9
55
87.8
56.7
93.7
54.3
82.7
58.6
78.1
50.7
82.1
52.2
80.8
58.9
75
49.8
71.5
43
71.7
40
73.4
52.7
PCPN
---------0.01
0.14
------0.09
0.63
0.42
0.02
0.06
---0.21
0.01
---------0.08
------------------------------------------------------------------0.01
1.69
----------------------
Soil temperature
2” depth
4” depth
Maximum
Minimum
Maximum
Minimum
81.7
58.8
77.4
61.2
75.9
59.6
73.2
61.6
78.5
64
74.9
64.6
81
65.9
76.7
66.7
84.2
64.6
79.7
65.8
86.3
61.6
81.4
63.5
88.2
65
83.4
66
81.8
71.5
78.7
71.4
78.6
68.9
76.1
69.4
80.7
64.4
77.3
65.8
79.1
64
76.7
65.2
78.2
61.7
76.1
63.4
79
60.2
76.7
62
71.5
61.3
69.6
63.2
78.9
59.3
76.3
60.7
81.7
58.2
78.3
60.4
80.4
59.1
77.4
61.2
84.4
62.1
80.8
63.6
73.5
64.1
71.8
65.8
80.4
58.9
77.3
61.2
82.1
57.1
78.2
59.8
83.9
59.7
80
61.8
85
62
80.8
63.9
82.2
67
78.3
67.8
87.7
66.1
83.4
67.3
86.4
69.3
82.2
70.2
84.7
71.7
81.1
71.9
89.4
67
84.6
68.5
89.6
65.3
84.8
67.3
90
67.2
84.9
68.8
91.7
69
86.4
70.2
92.6
69.4
87
70.8
89.2
72.6
84.2
73.3
91
67.3
85.8
69.6
89.7
63.8
84.5
67
85.7
67.5
80.8
69.3
89.5
72.9
84.3
73
91.7
69.9
85.7
71.1
90.9
71.5
85.4
72.6
84
68.2
80.1
70
90.8
67.6
85
69.6
89.7
66.6
84.1
69
84.8
68.2
81.3
70.3
81
62.1
78.1
64.7
78.8
62.2
74.7
64.3
75.5
65.4
73.8
66.5
79.6
67.1
77.6
68.5
76.7
60.4
75
63.1
73.6
58.3
71.5
61.1
75
63.1
72.8
64.2
8/20/07
8/21/07
8/22/07
8/23/07
8/24/07
8/25/07
8/26/07
8/27/07
8/28/07
8/29/07
8/30/07
8/31/07
9/1/07
9/2/07
9/3/07
9/4/07
9/5/07
9/6/07
9/7/07
9/8/07
9/9/07
9/10/07
9/11/07
9/12/07
9/13/07
9/14/07
9/15/07
9/16/07
9/17/07
9/18/07
9/19/07
9/20/07
9/21/07
9/22/07
9/23/07
9/24/07
9/25/07
9/26/07
9/27/07
9/28/07
9/29/07
9/30/07
71.9
74.3
84.1
78.6
75.1
74.8
78.6
79.2
91.1
73.7
76.3
80.9
82.8
83.6
82
85.9
91.5
89.5
77.5
81.3
73.5
60.6
63.5
59.9
73.9
66.4
57.8
68.5
76.2
86.5
76.3
76.4
85.5
74.2
80.2
89.7
80.5
65.1
69.2
66
71
78.3
57.2
61.1
65.6
65.4
66.2
59
46.9
49.5
67.4
61.7
48.5
44.1
48.6
51.6
53.1
53.1
60
71.8
63.3
47.9
47.4
51.5
42.4
40.7
38.3
45.1
36.2
35.1
45.4
60.4
55
50.6
57.6
45.1
40.7
50.4
62.7
42.8
41.8
39.4
35.9
61.5
0.27
---0.01
0.02
---0.51
------0.01
0.22
------------------------0.49
------0.08
0.2
0.01
---0.26
0.32
---------------0.03
0.16
------0.73
0.04
-------------
69.2
71.4
76.1
73.8
72.5
74.9
73.8
71.5
77.4
73.8
74.3
73.7
73.4
73.6
76.4
71.9
77.9
77
73.4
73.3
70.4
64.2
62.1
62
65
59.9
60.4
61.7
64.3
69.2
70.1
69.8
71.2
67.7
67
71.6
71.1
66.8
64.7
64.7
62.8
65.3
62.8
61.9
66
68.3
68.8
65
59.6
60.7
66
66.3
60.5
57.7
60.1
60.9
63.4
64.5
64.8
68.7
66.8
60.3
60
60.4
55.9
54.4
51.8
53.5
51.5
47.8
53.4
58
63
58.6
60.9
58.1
53.2
56.8
66.5
56.9
55
54.8
49.6
57.8
68.4
69.5
73.2
72.5
71.6
73.3
72.4
70.2
75
72.4
72.4
71.7
71.5
71.9
74.3
70.5
75.4
75
72.4
71.9
68.8
65.2
61.9
61.6
63.7
60.4
59.7
60.6
62.9
67.2
68.5
68.2
69.2
67.5
65.6
69.4
69.6
67.1
63.7
63.5
61.6
64.1
64.2
63
66.3
68.5
69.3
65.9
61.8
62.4
66.4
67.7
62.5
60.1
61.9
62.5
64.7
65.4
65.6
68.9
68.1
62.4
62
61.6
57.8
56.7
54
55.3
53.7
50.2
54.6
58.6
63.8
60
61.6
60.3
55.4
58.2
66.3
59.3
56.8
56.5
52.1
58.5