Quote:. . . three (fire blight resistant cultivars) have been named, Harvest Queen, Harrow
Delight, and Harrow Sweet.

Update on Harrow Fire Blight-resistant
Pear Selections and Cultivars

Dr. David M. Hunter, Pear Breeder
Agriculture and Agri-Food Canada, Southern Crop Protection and Food Research Center
Vineland Station, Ontario Canada L0R 2E0

Presented at the 42ndAnnual IDFTA Conference, February 20-24, 1999, Hamilton, Ontario.

Most commercial pear cultivars are susceptible to the bacterial disease fire blight (Erwinia
amylovora). The major objective of the pear breeding program at Harrow was to incorporate fire
blight resistance into high quality pear cultivars primarily for the fresh market. In order to allow
fruit production in areas where fire blight is present, a level of field resistance similar to, or
greater than, that of Kieffer is required.

The Harrow program, established in 1963, was a traditional breeding program involving
controlled hybridizations between selected parents. The resistance of advanced selections and
cultivars introduced from the program is derived from cultivars such as Seckel, Waite, Maxine,
Old Home, Farmingdale and Kieffer, or from species selections such asPyrus ussuriensis76 and
P. pyrifoliaNJ-1. When species selections were used, desirable fruit characteristics ofP.
communiswere recovered by back-crossing to selectedP. communiscultivars, especially Bartlett
(syn. William’s Bon Chretien). Harrow seedling selections were first used as pollen parents in
1972, and as seed parents in 1973. Several seedling populations have been generated using
Harrow selections as both pollen and seed parents.

Screening techniques were developed to identify fire blight-resistant seedlings. In the
greenhouse, the fire blight organism was injected into the shoot tip of actively growing seedlings
30-40 cm tall, and only the more resistant seedlings (i.e., those where the lesion extended less
than 25-30% of the total shoot length) were planted out in seedling orchards for field evaluations.
With the onset of fruiting, usually 5-7 years (sometimes up to 10 years) after planting out,
seedlings with desirable fruit characteristics were again screened for fire blight resistance by
inoculating actively growing shoot tips and assessing disease development. Natural fire blight
infections were also assessed in the field using the USDA rating system, in which 10 indicates no
infections while 1 indicates that the tree has been killed by fire blight. In general, a rating of 8
(equivalent to Kieffer) or higher is required for further evaluation. With ratings of 8 or 9,
infections which do not extend beyond current season’s growth can be expected, while ratings
below 7 indicate infections into previous season’s growth and older wood. On this scale, the
average rating for Bartlett at Harrow has been 3.9, indicating that severe infections leading to
limb or trunk damage can be expected most years.

Seedlings were evaluated for a number of fruit characteristics including flavor, texture, color,
fruit size and shape and ripening season, as well as for tree growth habit and productivity. Shelf
life, storage quality and processing capability were assessed in the laboratory. Winter hardiness
levels were determined following test winters or through controlled freezing tests, and all

Harrow advanced selections have a level of cold hardiness equal to or greater than Bartlett,
though few of the selections are as hardy as the fire blight-susceptible cultivar Flemish Beauty.

Selections placed in regional trials under a test number (prefixed by HW) are also evaluated in
advanced test orchards at Harrow and by other researchers. Grower members of the Ontario Fruit
Testing Association (OFTA) [formerly the Western Ontario Fruit Testing Association (WOFTA)]
have exclusive rights to test HW-numbered selections, subject to propagation-restriction
agreements, in commercial orchards. Data collected from all these sources are used to determine
whether a numbered selection is introduced, tested further or discarded. Virus testing of
advanced selections has been conducted at the Center for Plant Health in Saanichton, BC, and
true-to-name virus-indexed stock has been placed in repositories to provide a source of
propagating material.

With the implementation of the Plant Breeder’s Rights Act of Canada (1990), introductions are
first protected and subject to commercialization contracts. In the European Union, the agents are
Domaine de Castang S.A., St-Laurent-des-Vignes, 24100 Bergerac, France (for Harrow Sweet
pear only) and Star Fruits, 84430 Mondragon, France (other pear introductions). In North
America, Australia, New Zealand and Japan, commercialization rights to all pear introductions
have been granted to Inter-Plant Patent Marketing Inc., R.R. 2, Niagara-on-the-Lake, ON Canada
L0S 1J0.

To date, 25 selections have been placed in advanced trials. Of these, three (fire blight resistant
cultivars) have been named, Harvest Queen, Harrow Delight, and Harrow Sweet; three are in the
final stages of testing prior to naming, and nine selections require further evaluation. Other
selections have been discarded at Harrow because of unsuitability for local conditions, but some
are still being evaluated in other areas. All these selections have good to excellent resistance (but
not immunity) to natural fire blight infections, with ratings greater than 8.5 on the USDA scale.
Picking dates range from about 2 weeks before to 4 weeks after Bartlett, thus providing growers
with the opportunity to plant fire blight-resistant pears which fit into their own particular harvest
system.

Regional trials initiated in 1992 at 5 sites in Ontario provided important data for several
selections. A new regional trial will be planted in 1999 to further evaluate a number of Harrow
cultivars and selections on different rootstocks. This collaborative project involves the Ontario
Tender Fruit Producers Marketing Board, the Ontario Ministry of Agriculture, Food and Rural
Affairs, Nabisco Limited,Agriculture and Agri-Food Canada, and the University of Guelph,
Horticultural Research Institute of Ontario, and is being funded by the CanAdapt Program of the
Agricultural Adaptation Council.

Hybridizations and seedling evaluations at Harrow were directed by the following breeders:
R.E.C Layne (1963-1968), H.A. Quamme (1968-1980), F. Kappel (1983-1987) and D.M. Hunter
(1988-1995). The program was transferred to Vineland Station following the 1995 reorganization
in Agriculture and Agri-Food Canada, and D.M. Hunter is continuing the development of fire
blight-resistant pear selections using biotechnological methods. It is anticipated that transgenic
plants will be available for field evaluations by 2005.

The following are brief notes on the named introductions and numbered selections currently
being evaluated, presented in order of picking date.

HARROW DELIGHT
Bartlett x Purdue 80-51 (Early Sweet x Old Home).Harvested about August 10 at Harrow,
2 weeks before Bartlett. Fruit color is greenish-yellow with a red blush. Because it tends to drop
heavily as it matures, fruit should be picked while still green. If left on the tree until the
background color changes to yellow, shelf life is also greatly reduced. The tree consistently
produces good crops. Fruit size which is similar to Bartlett on unthinned trees is improved by
thinning. Even when the skin color is more green than yellow, flesh texture is very good, very
juicy and free of stone cells. Fruit flavor is rated as high as Bartlett. When processed as halves or
puree, Harrow Delight has had better-than-average ratings, but not as high as for Bartlett. Mature
trees have excellent resistance to fire blight (9.5 rating on the USDA scale), but this cultivar is
susceptible to pear psylla. Harrow Delight is pollen compatible with Harvest Queen, Bartlett,
Bosc and Anjou. This cultivar was released in 1981 and therefore there are no propagation
restrictions.

HW616
Harvest Queen x Harrow Delight.Fruit are picked about 10 days before Bartlett, between
Harrow Delight and Harvest Queen. An attractive yellow fruit, with good size (larger than
Harvest Queen, similar to Bartlett), smooth skin, fine texture, very good flavor, and
exceptionally juicy. The fresh fruit quality rating for HW616 is similar to that of Bartlett. As with
many other early season pears, the fruit will not keep for very long (probably no more than 4-
6 weeks) in cold storage, but it is an excellent selection for fresh market and roadside stands.
This selection is fire blight resistant (9.5 rating). HW616 does not appear to pollinate Bartlett,
but Bartlett may pollinate HW616. In a second test planting, precocity appears to be similar to
that of Bartlett with trees coming into production about 4 years after planting.

HW621
H6720-1.001 (Anjou x Farmingdale) x Harrow Delight.The fruit ripen in mid-August, about
10 days before Bartlett and slightly ahead of Harvest Queen. The fruit, slightly larger than
Bartlett, have an attractive, green-yellow ground color with a light blush on the exposed side.
The cream-colored flesh has excellent flavor and is very juicy. The fruit tends to be produced in
clusters of 4-5 fruit and thinning probably will be required. The tree has excellent resistance to
fire blight (9.7 rating). Some russetting of the fruit has been observed. Fruit of this selection have
been kept in cold storage for 8 weeks with no deterioration in fruit quality.

HW622
HW601 (Maxine x Beierschmidt) x Harrow Delight.Produces medium to heavy crops,
consistent from year to year with no evidence of biennial bearing. It is picked about 10 days
before Bartlett, between Harrow Delight and Harvest Queen. The medium-sized fruit are
produced in clusters of 3-4 fruit, so thinning may improve fruit size. When ripened, fruit have a
yellow background color with an attractive red blush. Fruit are typically pear-shaped with a
somewhat flattened calyx end. Flesh is white to cream-white with some small grit around the
core and just under the skin, and the texture is juicy, melting or buttery. Fruit have received good
to excellent ratings and can be kept in storage for about 6 weeks without severe breakdown.
Evaluations of processed product (as halves or puree) have been acceptable but ratings have been
lower than for Bartlett. The tree is tall, upright to spreading. Although there is an old fire blight
strike on the seedling tree, inoculations do not induce a severe disease response. Preliminary data
suggest that HW622 is reciprocally pollen incompatible with Bartlett.